Trends in Landfalling Tropical Cyclone–Induced Precipitation Over China

15 MARCH 2020 L I U A N D W A N G 2223

Trends in Landfalling Tropical Cyclone–Induced Precipitation over China

LU LIU State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

YUQING WANG International Paciﬁc Research Center and Department of Atmospheric Sciences, School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Honolulu, Hawaii, and State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

(Manuscript received 17 September 2019, in ﬁnal form 6 January 2020)

ABSTRACT

In this study, trends in landfalling tropical cyclone (TC)-induced precipitation over China during 1980–2017 and the involved possible mechanisms are analyzed. Consistent with previous studies, it is found that the total annual TC precipitation shows a distinct spatial distribution with a significant increasing trend in southeastern China but a decreasing trend in southern China. This characteristic is found to be related to the increase in both the annual TC precipitation frequency and the precipitation intensity per TC over southeastern China but to the decrease in the annual TC precipitation frequency over southern China. A noticeable northward shift of total landfalling TC-induced annual precipitation has been identified. It is shown that the precipitation induced by strong TCs (STCs) significantly increased in southern China, whereas that induced by weak TCs (WTCs) increased in southeastern China, with the latter dominating the northward shift of total landfalling TC-induced precipitation over mainland China. The increasing trend of STC-induced precipitation in southern China is found to be closely related to sufficient water vapor supply and the increase in average duration and intensity of STCs after landfall. The increasing trend of WTC-induced precipitation in southeastern China is related to the northward shift of the average landfalling position of WTCs and changes in the environmental conditions that are more favorable for TC maintenance and precipitation.

1. Introduction Knutson et al. 2010; Park et al. 2014; Zhang et al. 2016; Liu et al. 2020). Some studies have also shown that a In response to global warming, precipitation has positive relationship exists between TC-induced rainfall shown significant regional dependent trends in the rate and TC intensity (Rodgers et al. 2001; Lonfat et al. globe. For more than half of the global land, an in- 2004; Jiang 2012; Yu et al. 2017; M. Liu et al. 2019). creasing probability of intense precipitation events has Other studies have reported significant contributions by been documented by Groisman et al. (2005). A number landfalling TCs to both the annual total precipitation of weather systems can produce intensive precipitation and extreme precipitation events in the United States over land. The tropical cyclone (TC) is one of them. A (Knight and Davis 2009; Shepherd et al. 2007; Kunkel strong TC can produce torrential rainfall, leading to et al. 2010). floods and landslides after their landfall, which could East Asia is one of the regions that suffer the most cause loss of life and severe damage of properties (Karl severe damages from landfalling TCs. Several studies and Easterling 1999; Zhang et al. 2009). Many studies have investigated the changes in spatial distribution and have shown an increasing trend in the destructiveness of variability of heavy rainfall induced by landfalling TCs TCs due to the increasing trend in TC intensity and (Ren et al. 2006, 2007; Kim et al. 2006; Wu et al. 2007; lifetime from observations and climate model simula- Ying 2011a,b; Zhang et al. 2013). Kim et al. (2006) found tions (Knutson and Tuleya 2004; Emanuel 2005; 2 an abrupt increase in heavy rainfall ($100 mm day 1) Webster et al. 2005; Klotzbach 2006; Knutson et al. 2007; related to TCs over the Korean peninsula during August–September after the late 1970s. Ren et al. (2006, Corresponding author: Prof. Yuqing Wang, [email protected] 2007) investigated TC precipitation over China and

DOI: 10.1175/JCLI-D-19-0693.1 Ó 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2224 JOURNAL OF CLIMATE VOLUME 33 found a significant downward trend in annual TC precip- in landfalling TC-induced precipitation over mainland itation volume. Wu et al. (2007) studied the effect of TCs China and the involved possible mechanisms. The rest of on the total and extreme TC precipitation in Hainan Island the paper is organized as follows. Section 2 describes the and found that both the number of TCs affecting Hainan data and analysis methods. The temporal and spatial Island and the TC-induced precipitation and its contribu- characteristics of trends in the observed landfalling TC tion to the total precipitation decreased. However, both precipitation over mainland China are presented in the total amount of precipitation from the extreme rainfall section 3. Section 4 examines the trend characteristics of events and the number of extreme heavy precipitation TC precipitation in different categories and the involved days affected by TCs increased significantly. On average, possible mechanisms. The primary findings are sum- both the number of extreme rainfall days and the precip- marized in the last section. itation amount induced by each TC also increased significantly over Hainan Island. Based on a quantile regression 2. Data and analysis methods analysis of station data, Ying et al. (2011a) estimated the TC-induced precipitation trends over mainland China and The best-track TC dataset used in this study is ac- found that although the landfalling TC frequency de- quired from the Shanghai Typhoon Institute of China creased over China, especially over South China, both Meteorological Administration (STI/CMA), which in- precipitation per TC and maximum hourly precipitation cludes latitude and longitude of the TC center, TC in- induced by a TC increased significantly at stations in the tensity in terms of the maximum sustained 10-m wind southeast coastal region. They also found that the location speed, and central sea level pressure at 6-h intervals. TCs, of significant precipitation trends was related to mountains including tropical depressions (TD), that made landfall and coastline in southeastern China. However, in another over mainland China, including Hainan Island, during study, Ying et al. (2011b) found that there were insignifi- 1980–2017 are included in our analyses. In this study, the cant trends in extreme TC rainfall, such as the maximum STI/CMA best-track dataset is used as the primary TC TC precipitation and the maximum hourly precipitation data because relatively more observational data were over China during 1955–2006. available over mainland China when the postseason TC Zhang et al. (2013) further investigated the landfalling analysis was conducted to generate the best-track TC TC precipitation features over mainland China and the data. Actually, the annual postseason analysis of TC data contribution of TC rainfall to changes in the precipita- is performed by STI/CMA to reduce uncertainties and tion climate and the average rainfall per TC in the peak improve the accuracy using all available data, including TC season (July–September) during 1965–2009. They station observations, ship weather reports, automatic found that the TC rainfall accounted for more than 10% surface observations, synoptic charts, radiosonde data, of the summer rainfall in South and Southeast China, aircraft reconnaissance, satellite, coastal radar observa- even more than 40% along the southeast coastline, and tions, and the real-time TC warming advice from various the average rainfall per TC significantly increased in agencies (Ying et al. 2014). Note that TCs whose centers Southeast China south of the Yangtze River and east of remained offshore and did not make landfall over main- 1108E, which was consistent with the results of Ying land China were not considered in our analyses. et al. (2011a). Zhang et al. (2013) also found that the The daily precipitation dataset used in this study is increasing trends in the average rainfall per TC were not obtained from STI/CMA as well. Previous studies sim- accompanied by enhanced TC intensity, nor did they ply defined the TC precipitation as precipitation within a result from the slowdown of TC movement. Instead, radius of 550 km from the center of a TC (Englehart and they argued that the increasing trends in the average Douglas 2001) or 500 km from the center of a TC (Dare rainfall per TC in China might be associated with et al. 2012; Zhang et al. 2019). In this study, the objective changes in the East Asian summer monsoon activity synoptic analysis technique (OSAT) developed by Ren through modulating the moisture transport and other et al. (2006, 2007) is adopted to isolate the TC-induced synoptic forcing conditions. rainfall from the total daily precipitation; a similar Although previous studies have revealed many char- technique was also used in Zhang et al. (2013).TC acteristics of TC-induced precipitation over mainland precipitation can result from the TC eyewall and spiral China, including the long-term increasing trend in the rainbands, or from the interactions between the TC average rainfall per TC, the detailed spatial patterns and circulation and other local weather systems. TC rain- the contributions by different category TCs have not bands are generally asymmetric about the TC center. been examined, and the involved factors responsible for Therefore, the simple circle method is not good enough. the observed trends have not been well understood. In The OSAT method imitates the process by which a this study, we explore the spatial distribution of trend weather forecaster manually analyzes a synoptic map.

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2225

There are two primary steps: first, separating the daily study period. The frequency of landfalling TCs shows a precipitation into several independent rainbands, and significant decreasing trend (Fig. 1d); that is, the number second, according to the distance function between the of TCs making landfall over mainland China decreased in TC center and the distribution of the rainbands, dis- recent decades. Further, we calculated the frequency tinguishing which rainbands are related to the TC. The of landfalling TCs in the southern area and southeast- details of the method can be found in Ren et al. (2006, ern area (with 248N as the dividing line; Figs. 1e and 1f). 2007). Note that because having too few stations with The results show that the landfalling TC frequency in precipitation is not representative, the only cases that the southeastern area was stable, while the frequency in are considered in our analyses are those for which there the southern area experienced a significant decreasing were more than 30 stations at which daily precipitation trend during recent decades. Therefore, the decrease in was observed in a TC day. The TC precipitation is de- total landfalling TC frequency over mainland China was termined when the TC’s rainbands are over mainland contributed primarily by the decrease in frequency in the China, including Hainan Island, even if the center of the southern area. This suggests that the total annual pre- TC was still over the ocean but made landfall later. cipitation decrease could be primarily due to the signifi- The European Centre for Medium-Range Weather cant decrease in landfalling TCs over mainland China, Forecasts (ECMWF) interim reanalysis (ERA-Interim) especially in southern China. data at the horizontal resolution of 0.75830.758 (Dee Figure 2 shows the time series and trend in the average et al. 2011) are used to examine changes in large-scale precipitation per landfalling TC. There is a significant environmental conditions responsible for the observed increasing linear trend of the average precipitation per changes in the precipitation characteristics of landfalling landfalling TC over mainland China as a whole (Fig. 2a) TCs over mainland China. The sea surface temperature with statistical significance over the 95% confidence (SST) data are obtained from NOAA’s Optimum level. This means that the precipitation intensity per Interpolation Sea Surface temperature (OISST), which landfalling TC increased significantly during 1980–2017, provide a series of global analysis products including the especially in the southeastern coastal region over daily SST at the resolution of 0.25830.258. The soil mainland China (Fig. 2b). However, over Hainan Island, moisture is obtained from the NOAA Gridded Climate the precipitation per landfalling TC shows a significant Dataset, which has a horizontal resolution of 0.5830.58. decreasing trend. We also analyzed the trend of the TC precipitation per landfalling TC per day, which shows a significant increasing trend over mainland China as a 3. Characteristics of landfalling TC precipitation whole as well (Fig. 3a). The trend also displays a spatial Figure 1a shows the spatial distribution of the average distribution with the largest increasing trend in the annual precipitation induced by landfalling TCs over southeastern coastal area (Fig. 3b), which contributes to mainland China during 1980–2017. Consistent with pre- the increase in the average precipitation per landfalling vious studies (Ren et al. 2006; Zhang et al. 2013), large TC in the region (Fig. 2b). The trend in annual TC TC precipitation is mainly located in the southern and rainfall days (frequency) shows a clear transition near southeastern China, including Guangxi, Guangdong, and 248–258N—namely, an increasing trend over southeast- Fujian provinces, and Hainan Island. The time series of ern China and a decreasing trend over southern China total annual TC precipitation over mainland China as a (Fig. 3c). Therefore, both the annual precipitation fre- whole presents a slightly decreasing linear trend (Fig. 1b), quency and the average precipitation per TC per day which is consistent with the results of Ren et al. (2006), increased over southeastern China, leading to the large who found that the total volume of landfalling TC pre- increasing trend in total TC precipitation over south- cipitation over China was slightly decreasing. However, eastern China (Fig. 1c). The decreasing trend in the the trend of the annual landfalling TC precipitation over frequency of landfalling TCs (Fig. 1d) offsets the in- mainland China shows a distinct spatial distribution creasing trend of the average precipitation per TC per (Fig. 1c). The annual TC precipitation increased signifi- day over southern China (Fig. 3a). This leads to the cantly over southeastern China and decreased notably decreasing trend in the total TC precipitation over over southern China, including Hainan Island (Fig. 1c). southern China as seen in Fig. 1c. Wu et al. (2005) Comparing Figs. 1a and 1c,wecanseethatthemaximum found a considerable decreasing trend of TCs in the increasing trend in the annual TC precipitation occurs in South China Sea, leading to fewer rainfall days of the northern area and the maximum decreasing trend landfalling TCs in the southern coastal area over main- occurs in the southern area of the large precipitation re- land China. In addition, the deceasing trends in both the gion, indicating a northward shift in landfalling TC- average precipitation per TC per day (Fig. 3b) and the induced precipitation over mainland China during the annual frequency of TC precipitation days (Fig. 3c) give

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2226 JOURNAL OF CLIMATE VOLUME 33

FIG. 1. (a) Spatial distribution of the landfalling TC-induced annual precipitation averaged during 1980–2017 2 over China (mm yr 1). (b) Time series and trend of the landfalling TC-induced total annual precipitation averaged 2 over China during 1980–2017 (mm yr 1). (c) Spatial distribution of trends in the landfalling TC-induced annual 2 precipitation over China during 1980–2017 (mm yr 1). Also shown are time series and trend of the landfalling TC frequency over (d) China mainland, (e) the southern area, and (f) the southeastern area during 1980–2017. The dashed, solid, and blue curves in (b), (d), (e), and (f) indicate the raw data, 5-yr running mean, and the corresponding linear trends, respectively. Regions with trends that are signiﬁcant over 95% conﬁdence level are shown with dots in (c).

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2227

21 FIG. 2. (a) Time series and trend of precipitation (mm yr ) per landfalling TC averaged over China during 1980– 2 2017. (b) Spatial distribution of trend in total precipitation (mm yr 1) per landfalling TC over China during 1980– 2017. The dashed, solid, and blue curves in (a) indicate the raw data, the 5-yr running mean, and the corresponding linear trend, respectively. Regions with trends that are signiﬁcant over 95% conﬁdence level are shown with dots in (b).

rise to a significant decrease in the total TC precipitation by STCs. Note that precipitation induced by WTCs is over Hainan Island (Fig. 1c). This is consistent with the generally weaker than that induced by STCs. results of Wu et al. (2007), who found that the number of Since the spatial distributions of STC and WTC pre- TCs impacting Hainan Island significantly decreased. cipitation are different, it is interesting to examine the spatial pattern of their respective trends in the study period. Figure 5 presents the time series and the trends of 4. Characteristics of strong and weak TC average precipitation per STC and average precipitation precipitation per WTC, respectively, during 1980–2017. Consistent with We further classify landfalling TCs into strong TCs the average precipitation per TC (Fig. 2a), STC precipi- 2 (STCs; with sustained maximum wind speed $ 32 m s 1, tation also shows a significant increasing trend with sta- including typhoons, severe typhoons, and super- tistical significance over 95% confidence level (Fig. 5a), typhoons) and weak TCs (WTCs; with sustained maxi- indicating that precipitation induced by a STC increased 2 mum wind speed , 32 m s 1, including tropical storms, in the study period. The trends in STC precipitation are severe tropical storms, and tropical depressions) at positive over mainland China but negative over Hainan landfall. The TDs are included here because, on one Island (Fig. 5b). The most significant increase in STC hand, TDs in the STI/CMA best-track dataset were, to precipitation occurs in the southern coastal area (mainly some extent, reliable based on the description of the in Guangdong and Guangxi provinces), namely the region STI/CMA best-track data as mentioned in section 2;on with the maximum rainfall per STC shown in Fig. 4a.This the other hand, the precipitation induced by TDs could indicates that the precipitation induced by STCs signifi- be very large when they interacted with some favor- cantly increased over mainland China, especially in the able weather systems. Thus, the precipitation induced southern coastal area, but decreased over Hainan Island. by TDs is also important. The spatial distributions of The average precipitation per WTC shows no signifi- precipitation induced by STCs and WTCs are shown in cant trend over mainland China (Fig. 5c). This is pri- Figs. 4a and 4b, respectively. Precipitation induced by marily due to the cancellation of the decreasing trend in STCs is large in the southern coastal area, such as the southern coastal area and the increasing trend in the Guangxi, Guangdong, and Hainan provinces (Fig. 4a), southeastern coastal area of mainland China (Fig. 5d). It and slightly south of the maximum in the total TC pre- is interesting to note that significant increasing trends cipitation shown in Fig. 1a. Precipitation induced by primarily occurred in Fujian and Zhejiang provinces, WTCs is generally large in the southern and southeastern north of the peak WTC precipitation (Fig. 4b). This coastal area, including eastern Guangdong and Fujian means that WTC-induced precipitation shifted north- provinces (Fig. 4b) and is to the northeast of that induced ward in the study period, resulting in an increase in WTC

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2228 JOURNAL OF CLIMATE VOLUME 33

21 FIG. 3. (a) Time series and trend of precipitation (mm yr ) per landfalling TC per day averaged over China 2 during 1980–2017. (b) Spatial distribution of trend in averaged precipitation (mm yr 1) per landfalling TC per 2 day over China during 1980–2017. (c) Trends in TC precipitation frequency (TC precipitation; days yr 1). The dashed, solid, and blue curves in (a) indicate the raw data, the 5-yr running mean, and the corresponding linear trend, respectively. Regions with trends that are significant over 95% confidence level are shown with dots in (b) and (c). precipitation in the southeastern coastal area and a de- and 6b display the average water vapor and vapor flux crease in the southern coastal area (Fig. 5d). This is in vertically integrated between 1000 and 700 hPa and their sharp contrast to the STC-induced precipitation, which trends during 1980–2017. The southern coastal area of shows that the maximum increasing trend almost in the mainland China, where large STC precipitation occurred region coincided with peak STC precipitation. This in- (Fig. 4a), is perennially covered by high low-level water dicates that the northward shift of total landfalling TC vapor content and large moisture flux convergence be- precipitation over mainland China (Fig. 1c) is mainly tween the southwesterly flow with high moisture content contributed by the northward shift of WTC-induced from the Bay of Bengal and southeasterly flow with plenty precipitation. of water vapor from the western North Pacific. The area is To understand the possible mechanisms responsible for very conducive to precipitation induced by STCs. The the overall increasing trend in STC precipitation, we ex- water vapor in this area increased significantly in the study amined the large-scale environmental conditions and their period (Fig. 6b), which favored the increase in STC- corresponding trends. It is found that in addition to some induced precipitation. In addition, an increasing trend in other favorable dynamic and thermodynamic conditions divergence in the upper troposphere occurred in the (not shown), the atmospheric moisture supply seems to southern area and neighboring seas (Fig. 6c)andanin- play a key role in enhancing STC precipitation. Figures 6a creasing trend in ascending motion (Fig. 6d) appeared at

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2229

21 FIG. 4. Spatial distributions of the averaged annual precipitation (mm yr ) induced by (a) strong landfalling TCs and (b) weak landfalling TCs over China during 1980–2017 (see text for more details).

500 hPa. Both are conducive to the maintenance of TC significant increasing trend in the study period (Fig. 7b). intensity and thus contribute to the decrease in overland Therefore, no matter whether they were STCs or WTCs, the intensity weakening rate and the increase in mean over- intensity of TCs at landfall over mainland China increased land duration of landfalling TCs (e.g., Park et al. 2011). significantly in recent decades. This increasing trend is Meanwhile, both the landfall intensity (Fig. 6e) and du- consistent with the significant warming trend in SST in the ration after landfall (Fig. 6f) of STCs increased noticeably, coastal oceans near East Asia, particularly offshore of with statistical significance over the 90% confidence level. mainland China (Fig. 7c). The near-surface air temperature This is also conducive to increasing precipitation of STCs. (Fig. 7d) and soil moisture (Fig. 7e) also show increasing Previous studies have suggested that there was some re- trends, particularly in the southeastern coastal area of lationship between TC-induced rainfall rate and TC in- mainland China, providing more favorable thermodynamic tensity (Rodgers et al. 2001; Lonfat et al. 2004; Jiang 2012; conditions to slow down the weakening of TCs after landfall. Yu et al. 2017; M. Liu et al. 2019). Yu et al. (2017) analyzed Previous studies have demonstrated that the soil moisture the rainfall distribution in TCs making landfall over and temperature are critical for TC maintenance and TC mainland China and revealed that, on average, axisym- precipitation over land (Tuleya and Kurihara 1978; Tuleya metric rainfall was closely related to TC intensity. Stronger et al. 1984; Tuleya 1994; Shen et al. 2002; Zhang et al. 2011; TCs produce more averaged total rainfall, larger averaged L. Liu et al. 2019). As shown in Tuleya (1994), warm land rain areas, and higher averaged rain rates. M. Liu et al. surface and high soil moisture are favorable for surface (2019) also showed that TCs with high intensity tended to enthalpy flux and thus may slow down the weakening of a produce high rainfall rates, especially toward the storm TC after landfall. Zhang et al. (2011) conducted several center. Therefore, the sufficient water vapor supply and sensitivity numerical experiments and found that both the the increase in both duration after landfall and the increase latent and sensible heat flux sustained the landfalling TCs in storm intensity at landfall are all responsible for the and maintained the spiral structure of rainbands. increasing trend in STC precipitation in the southern In addition, the low-level vertical wind shear between coastal area of mainland China except over Hainan Island. 850 and 1000 hPa shows a significant decreasing trend over The northward shift of WTC precipitation is mainly southeastern China (Fig. 7f), which provides a favorable due to the northward shift of mean landfalling location dynamical environmental condition conducive to TC in- of WTCs (Fig. 7a) and changes in favorable environ- tensification and maintenance. Note that the deep-layer mental conditions, including surface conditions and vertical wind shear between 850 and 200 hPa was also an- low-level vertical wind shear. The average landfalling alyzed and the results showed a decreasing trend to the latitude of WTCs shows a clear increasing trend (Fig. 7a) north of approximately 338N over mainland China, but the with statistical significance over 90% confidence level. trend in the region affected by landfalling TCs was not The average landfalling latitude increased from about statistically significant (figure not shown). Wang et al. 228N to about 248N in the study period. In addition to (2015) compared the correlation between TC intensity the northward shift of the average landfalling location, change and vertical wind shear in various vertical layers the average intensity of landfalling WTCs also shows a over the WNP. They found that the low-level shear

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2230 JOURNAL OF CLIMATE VOLUME 33

21 FIG. 5. Time series and trends (mm yr ) of (a) strong TC–induced precipitation per TC and (c) weak TC– 2 induced precipitation per 1980–2017 averaged over China. Also shown are spatial distributions of trends (mm yr 1) of (b) STC precipitation per TC and (d) WTC precipitation per TC during 1980–2017. The dashed, solid, and blue curves in (a) and (c) indicate the raw data, 5-yr running mean, and the corresponding linear trend, respectively. Regions with trends that are significant over 95% confidence level are shown with dots in (b) and (d). between 850 (or 700) and 1000 hPa was more destructive to and the best-track TC data obtained from STI/CMA are TCs than the commonly used deep-layer vertical wind used to explore the characteristics of the landfalling TC- shear between 200 and 850 hPa in the active typhoon sea- induced precipitation and the precipitation per land- son over the WNP. As a result, the combination of the falling TC after landfall over China during 1980–2017. northward shift of the average landfalling position of WTCs The total annual TC precipitation over China as a whole and the more favorable dynamic and thermodynamic shows a decreasing trend primarily due to the decreasing conditions led to the increasing WTC-induced precipitation trend in the frequency of landfalling TCs during 1980– in the southeastern coastal area of mainland China. This 2017, which is consistent with the results of Ren et al. also explains why the increasing trend of WTC precipita- (2006). It is found that the total annual TC precipitation tion occurred north of the maximum WTC precipitation shows a distinct spatial distribution with a significant and the dominant contribution by WTCs to the northward increasing trend in southeastern China but a decreasing shift of the total landfalling TC precipitation. trend in southern China. This increasing to the north and decreasing to the south are found to be related to the increase in both the annual TC precipitation frequency 5. Conclusions (annual average TC precipitation days) and the average In this study, the daily TC precipitation dataset pro- precipitation per TC per day, over southeastern China, duced using the OSAT method (Ren et al. 2006, 2007) and to the decrease in the annual TC precipitation

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2231

21 FIG. 6. Spatial distributions of (a) water vapor mixing ratio (shading; kg kg ) and vapor flux (vectors; kg 2 2 2 2 2 mkg 1 s 1) integrated from 1000 to 700 hPa, (b) trends in water vapor mixing ratio (shading; 10 2 gkg 1 yr 1) 2 2 2 integrated from 1000 to 700 hPa, (c) upper-tropospheric divergence (10 6 s 1 yr 1) at 200 hPa, and (d) vertical 2 2 motion at 500 hPa (Pa s 1 yr 1) during 1980–2017. Also shown are time series and trends of (e) averaged landfalling 2 intensity (m s 1) and (f) duration after landfall (h) of STCs over China during 1980–2017. Regions with trends that are significant over 90% confidence level are shown with dots in (b)–(d). The dashed, solid, and blue curves in (e) and (f) indicate the raw data, the 5-yr running mean, and the corresponding linear trend, respectively.

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2232 JOURNAL OF CLIMATE VOLUME 33

FIG. 7. Time series and trends of (a) averaged landfalling latitude (8N) and (b) averaged landfalling intensity 2 2 (m s 1) of WTCs over China during 1980–2017; spatial distributions of trends in (c) SST (K yr 1), (d) air tem- 2 2 2 perature at 950 hPa (K yr 1), (e) soil moisture (g kg 1 yr 1), and (f) vertical wind shear between 1000 and 850 hPa 2 2 (m s 1 yr 1) during 1980–2017. The dashed, solid, and blue curves in (a) and (b) indicate the raw data, the 5-yr running mean, and the corresponding linear trend, respectively. Regions with trends that are signiﬁcant over 90% conﬁdence level are shown with dots in (c)–(f).

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2233 frequency over southern China. In addition, a northward precipitation per TC and the annual frequency of TC shift in precipitation induced by landfalling TCs over precipitation days over the past decades. Wu et al. mainland China during recent decades has been identified. (2007) found that the number of TCs impacting Hainan We have further classified landfalling TCs into STCs and Island significantly decreased. Therefore, the decreas- WTCs to examine the differences in their precipitation ing trend in landfalling induced precipitation over characteristics over mainland China. Some interesting new Hainan Island is most likely a result of the decreasing findings include a noticeable northward shift in the average landfilling TC frequency. In addition, the decreasing landfalling location of WTCs and their associated precip- trend in the average precipitation per TC over Hainan itation, and an overall increasing trend in landfalling in- Island might be partially due to the decrease in TC tensity of both STCs and WTCs. It is shown that the intensity at landfall and unfavorable environmental precipitation induced by STCs mainly concentrated in the conditions. For example, Wang et al. (2013) found that southern coastal area, slightly south of the maximum total due to the increase in the tropical Indian Ocean SST, TC precipitation, while the precipitation induced by WTCs the lower-level anomalous anticyclone occurred over is mainly located in the southeastern coastal area over South China Sea, which was unfavorable for TC genesis mainland China, coinciding with the region of total TC and intensification over the South China Sea. This is ev- precipitation. Moreover, the STC precipitation shows an ident by a trend of decreasing ascending motion in the increasing trend in most regions with large STC precipi- western South China Sea seen in Fig. 6d.Nevertheless, tation over mainland China, especially in southern China. because of the small area of the island and the sensitive The location of WTC-induced precipitation is east and regional climate patterns over Hainan Island, a more north of that of STC-induced precipitation and shows a detailed analysis on the possible mechanism responsible decreasing trend in the southern coastal area and an in- for the observed decreasing trend of landfalling TC- creasing trend in the southeastern coastal area of mainland induced precipitation over Hainan Island is reserved China. The most significant increasing trend occurred for a future study. north of the peak precipitation area induced by WTCs, Note that this study has focused on the analysis of long- indicating a noticeable northward shift of the WTC- term trends in the observed precipitation induced by induced precipitation in the study period. These results landfalling TCs over mainland China based on data be- demonstrate that the northward shift of total landfalling tween 1980 and 2017. Because the limited period was an- TC precipitation is mainly contributed by the WTC pre- alyzed due to TC precipitation data quality, the northward cipitation primarily due to the northward shift of land- shift in TC precipitation could be partly contributed by the falling location of WTCs. decadal/interdecadal variations, which need further in- Results from further analyses indicate that both the vestigations. However, a recent study by Liu et al. (2020) intensity at landfall and the duration after landfall of pointed out that the landfalling TC activity over mainland STCs increased noticeably. The region of STC pre- China seems not to be significantly modulated by the cipitation is perennially located in the convergence decadal/interdecadal variations because several in- zone with high humidity in the lower troposphere. terdecadal shifts identified in other climate parameters Water vapor in the area increased significantly in the did not appear in landfalling TC characteristics over study period, providing more water vapor supply for mainland China. Nevertheless, results from this study im- TC intensification/maintenance and precipitation. In plyanincreasingstressofpotential landfalling TC-induced contrast, WTCs show a significant increasing trend in precipitation in the populated southeastern coastal region their average landfall latitude, leading to a northward of mainland China if the trend continues in the near future. shift of WTC-induced precipitation. Moreover, the increasing intensity of WTCs at landfall and the in- Acknowledgments. The authors thank three anony- creasing SST in the coastal oceans, the increase in land mous reviewers for helpful review comments and Dr. surface soil moisture and temperature, and the de- Fumin Ren for providing the TC-induced precipitation crease in low-level vertical wind shear over south- dataset over China in this study. This study has been eastern and eastern China provide more favorable supported in part by the National Key R&D Program of dynamic and thermodynamic conditions for WTCs to China under Grants 2017YFC1501602 and in part by survive longer after landfall, leading to the increase in National Natural Science Foundation of China under WTC precipitation. Grants 41675044, 41705027, 41730960, and 41875114. Note that there was a remarkable decreasing trend The TC best-track data were obtained from STI/CMA in landfalling TC-induced precipitation over Hainan Island, (http://tcdata.typhoon.org.cn). The ECMWF data used regardless of STCs or WTCs. We found that this is mainly in this study were obtained online (http://apps.ecmwf.int/ due to the significant decreasing trend in both the average datasets/).The soil moisture dataset used in this study was

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 2234 JOURNAL OF CLIMATE VOLUME 33 obtained online (https://www.esrl.noaa.gov/psd/data/ ——, Y. Wang, R.-F. Zhan, J. Xu, and Y. Duan, 2020: Increasing gridded/data.cpcsoil.html). All figures were produced using destructive potential of landfalling tropical cyclones over China. the NCAR Command Language (NCL). J. Climate,inpress,https://doi.org/10.1175/JCLI-D-19-0451. Liu, M., G. A. Vecchi, J. A. Smith, and T. R. Knutson, 2019: Causes of large projected increases in hurricane precipitation rates REFERENCES with global warming. npj Climate Atmos. Sci., 2, 38, https:// doi.org/10.1038/S41612-019-0095-3. Dare, R. A., N. E. Davidson, and J. L. McBride, 2012: Tropical cy- Lonfat, M., Jr., F. D. Marks, and S. S. Chen, 2004: Precipitation clone contribution to rainfall over Australia. Mon. Wea. Rev., distribution in tropical cyclones using the Tropical Rainfall 140, 3606–3619, https://doi.org/10.1175/MWR-D-11-00340.1. Measuring Mission (TRMM) Microwave Imager: A global Dee, D. P., and Coauthors, 2011: The ERA-Interim reanalysis: perspective. Mon. Wea. Rev., 132, 1645–1660, https://doi.org/ Configuration and performance of the data assimilation sys- 10.1175/1520-0493(2004)132,1645:PDITCU.2.0.CO;2. tem. Quart. J. Roy. Meteor. Soc., 137, 553–597, https://doi.org/ Park, D.-S. R., C.-H. Ho, J.-H. Kim, and H.-S. Kim, 2011: Strong landfall 10.1002/qj.828. typhoons in Korea and Japan in a recent decade. J. Geophys. Res., Emanuel, K., 2005: Increasing destructiveness of tropical cyclones 116, D07105, https://doi.org/10.1029/2010JD014801. over the past 30 years. Nature, 436, 686–688, https://doi.org/ ——, ——, and ——, 2014: Growing threat of intense tropical cy- 10.1038/nature03906. clones to East Asia over the period 1977–2010. Environ. Res. Englehart, P. J., and A. V. Douglas, 2001: The role of eastern North Lett., 9, 014008, https://doi.org/10.1088/1748-9326/9/1/014008. Pacific tropical storms in the rainfall climatology of western Mexico. Ren, F., G. Wu, W. Dong, X. Wang, Y. Wang, W. Ai, and W. Li, 2006: Int. J. Climatol., 21, 1357–1370, https://doi.org/10.1002/joc.637. Changes in tropical cyclone precipitation over China. Geophys. Res. Groisman, P. Ya., R. W. Knight, D. R. Easterling, T. R. Karl, G. C. Lett., 33, L20702, https://doi.org/10.1029/2006GL027951. Hegerl, and V. N. Razuvaev, 2005: Trends in intense precipi- ——, Y. Wang, X. Wang, and W. Li, 2007: Estimating tropical tation in the climate record. J. Climate, 18, 1326–1350, https:// cyclone precipitation from station observations. Adv. Atmos. doi.org/10.1175/JCLI3339.1. Sci., 24, 700–711, https://doi.org/10.1007/s00376-007-0700-y. Jiang, H., 2012: The relationship between tropical cyclone intensity Rodgers, E. B., R. F. Adler, and H. F. Pierce, 2001: Contribution of change and the strength of inner-core convection. Mon. Wea. Rev., tropical cyclones to the North Atlantic climatological rainfall as 140, 1164–1176, https://doi.org/10.1175/MWR-D-11-00134.1. observed from satellites. J. Appl. Meteor., 40, 1785–1800, https:// Karl, T. R., and D. R. Easterling, 1999: Climate extremes: Selected doi.org/10.1175/1520-0450(2001)040,1785:COTCTT.2.0.CO;2. review and future research directions. Climatic Change, 42, Shen, W., I. Ginis, and R. E. Tuleya, 2002: A numerical investigation 309–325, https://doi.org/10.1023/A:1005436904097. of land surface water on landfalling hurricanes. J. Atmos. Sci., Kim, J.-H., C.-H. Ho, M.-H. Lee, J.-H. Jeong, and D. Chen, 2006: 59, 789–802, https://doi.org/10.1175/1520-0469(2002)059,0789: Large increase in heavy rainfall associated with tropical cy- ANIOLS.2.0.CO;2. clone landfalls in Korea after the late 1970s. Geophys. Res. Shepherd, J. M., A. Grundstein, and T. L. Mote, 2007: Quantifying Lett., 33, L18706, https://doi.org/10.1029/2006GL027430. the contribution of tropical cyclones to extreme rainfall along Klotzbach, P. J., 2006: Trends in global tropical cyclone activity the coastal southeastern United States. Geophys. Res. Lett., over the past twenty years (1986–2005). Geophys. Res. Lett., 34, L23810, https://doi.org/10.1029/2007GL031694. 33, L10805, https://doi.org/10.1029/2006GL025881. Tuleya, R. E., 1994: Tropical storm development and decay: Knight, D. B., and R. E. Davis, 2009: Contribution of tropical cy- Sensitivity to surface boundary conditions. Mon. Wea. Rev., clones to extreme rainfall events in the southeastern United 122, 291–304, https://doi.org/10.1175/1520-0493(1994) States. J. Geophys. Res., 114, D23102, https://doi.org/10.1029/ 122,0291:TSDADS.2.0.CO;2. 2009JD012511. ——, and Y. Kurihara, 1978: A numerical simulation of the landfall Knutson, T. R., and R. E. Tuleya, 2004: Impact of CO2-induced of tropical cyclones. J. Atmos. Sci., 35, 242–257, https://doi.org/ warming on simulated hurricane intensity and precipitation: 10.1175/1520-0469(1978)035,0242:ANSOTL.2.0.CO;2. Sensitivity to the choice of climate model and convective pa- ——, M. A. Bender, and Y. Kurihara, 1984: A simulation study of the rameterization. J. Climate, 17, 3477–3495, https://doi.org/ landfall of tropical cyclones. Mon. Wea. Rev., 112, 124–136, https:// 10.1175/1520-0442(2004)017,3477:IOCWOS.2.0.CO;2. doi.org/10.1175/1520-0493(1984)112,0124:ASSOTL.2.0.CO;2. ——, J. J. Sirutis, S. T. Garner, I. M. Held, and R. E. Tuleya, 2007: Wang, L., R. H. Huang, and R. Wu, 2013: Interdecadal variability in Simulation of the recent multidecadal increase of Atlantic tropical cyclone frequency over the South China Sea and its asso- hurricane activity using an 18-km-grid regional model. Bull. ciationwiththeIndianOceanseasurfacetemperature.Geophys. Amer. Meteor. Soc., 88, 1549–1565, https://doi.org/10.1175/ Res. Lett., 40, 768–771, https://doi.org/10.1002/grl.50171. BAMS-88-10-1549. Wang, Y., Y. Rao, Z.-M. Tan, and D. Schönemann, 2015: A statistical ——, and Coauthors, 2010: Tropical cyclones and climate change. analysis of the effects of vertical wind shear on tropical cyclone Nat. Geosci., 3, 157–163, https://doi.org/10.1038/ngeo779. intensity change over the western North Pacific. Mon. Wea. Rev., Kunkel, K. E., D. R. Easterling, D. A. Kristovich, B. Gleason, 143, 3434–3453, https://doi.org/10.1175/MWR-D-15-0049.1. L. Stoecker, and R. Smith, 2010: Recent increases in U.S. heavy Webster, P. J., G. J. Holland, J. A. Curry, and H. R. Chang, 2005: precipitation associated with tropical cyclones. Geophys. Res. Changes in tropical cyclone number, duration, and intensity Lett., 37,L24706,https://doi.org/10.1029/2010GL045164. in a warming environment. Science, 309, 1844–1846, https:// Liu, L., J. Xu, Y. Wang, and Y.-H. Duan, 2019: Contribution of re- doi.org/10.1126/science.1116448. cycling of surface precipitation to landfalling tropical cyclone Wu, L., B. Wang, and S. Geng, 2005: Growing typhoon influence on rainfall: A modeling study for Typhoon Utor (2013). J. Geophys. East Asia. Geophys. Res. Lett., 32, L18703, https://doi.org/ Res. Atmos., 124, 870–885, https://doi.org/10.1029/2018JD029380. 10.1029/2005GL022937.

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC 15 MARCH 2020 L I U A N D W A N G 2235

Wu, Y., S. Wu, and P. Zhai, 2007: The impact of tropical cyclones Zhang, J., L. Wu, F. Ren, and X. Cui, 2013: Changes in tropical on Hainan Island’s extreme and total precipitation. Int. cyclone rainfall in China. J. Meteor. Soc. Japan, 91, 585–595, J. Climatol., 27, 1059–1064, https://doi.org/10.1002/joc.1464. https://doi.org/10.2151/jmsj.2013-502. Ying, M., B. Chen, and G. Wu, 2011a: Climate trends in tropical cyclone- Zhang, Q., L. Wu, and Q. Liu, 2009: Tropical cyclone damages in induced wind and precipitation over mainland China. Geophys. Res. China 1983–2006. Bull. Amer. Meteor. Soc., 90, 489–496, Lett., 38, L01702, https://doi.org/10.1029/2010GL045729. https://doi.org/10.1175/2008BAMS2631.1. ——, Y.-H. Yang, B.-D. Chen, and W. Zhang, 2011b: Climatic Zhang, W., and Coauthors, 2016: Inﬂuences of natural variability and variation of tropical cyclones affecting China during the past anthropogenic forcing on the extreme 2015 accumulated cyclone 50 years. Sci. China Earth Sci., 54, 1226–1237, https://doi.org/ energy in the western north Paciﬁc. Bull. Amer. Meteor. Soc., 97, 10.1007/s11430-011-4213-2. S131–S135, https://doi.org/10.1175/BAMS-D-16-0146.1. ——, W. Zhang, H. Yu, X. Lu, J. Feng, Y. Fan, Y. Zhu, and D. Chen, ——,G.Villarini,G.A.Vecchi,andH.Murakami,2019:Rainfallfrom 2014: An overview of the China Meteorological Administration tropical cyclone database. J. Atmos. Oceanic Technol., 31,287– tropical cyclones: High-resolution simulations and seasonal fore- 301, https://doi.org/10.1175/JTECH-D-12-00119.1. casts. Climate Dyn., 52, 5269–5289, https://doi.org/10.1007/s00382- Yu, Z., Y. Wang, H. Xu, N. Davidson, Y. Chen, Y. Chen, and 018-4446-2. H. Yu, 2017: On the relationship between intensity and rainfall Zhang, Y., C. Cassardo, C. Ye, M. Galli, and N. Vela, 2011: The role of distribution in tropical cyclones making landfall over China. the land surface processes in the rainfall generated by a landfall J. Appl. Meteor. Climatol., 56, 2883–2901, https://doi.org/ typhoon: A simulation of the Typhoon Sepat (2007). Asia-Pac. 10.1175/JAMC-D-16-0334.1. J. Atmos. Sci., 47, 63–77, https://doi.org/10.1007/s13143-011-1006-7.

Unauthenticated | Downloaded 09/28/21 07:53 PM UTC