Annual Journal of Hydraulic Engineering, JSCE, Vol.60, 2016, February

IMPACT ASSESSMENT OF HUMAN ACTIVITIES AND CLIMATE CHANGE ON ANNUAL RUNOFF IN THE KAMO RIVER BASIN

Maochuan HU1, Takahiro SAYAMA2, Shusuke TAKAHASHI1 and Kaoru TAKARA3

1 Student Member of JSCE, Department of Civil and Earth Resources Engineering, Graduate School of Engineering, University (Kyoto daigaku-Kastura, Nishikyo-ku, Kyoto 615-8530, ) 2Member of JSCE, Dr. of Eng., Disaster Prevention Research Institute, Kyoto University (Gokasho, Uji, Kyoto 611-0011, Japan) 3Fellow of JSCE, Dr. of Eng., Disaster Prevention Research Institute, Kyoto University (Gokasho, Uji, Kyoto 611-0011, Japan)

According to an observation record, long-term discharge at Fukakusa station in the Kamo River basin has been decreasing, which may affect water-related landscapes and the ecosystem. This study conducts a forensic analysis to investigate the dominant reasons for the streamflow reduction and attempt to quantify the contribution of each factor based on water balance analysis, trend analysis and hydrologic model simulation. The results suggest that the decreasing trend is primarily caused by the increase of drainage areas of the sewage system in Kyoto city and the reduction of intake from to the Kamo River. These effects diminish the impact of slight increase in the annual precipitation and suppress the increase in evapotranspiration in the Kamo River basin.

Key Words: climate change, human activities, hydrological modeling, water balance analysis, trend test, the Kamo River

1. INTRODUCTION amenities, especially in dry season, it is necessary to maintain water level. Also, the decrease in Kyoto is a historical city famous for many streamflow poses a potential threat for the cultural heritages and also water-related landscapes, ecosystem including freshwater habitat. Thus, it is whose large part of water is distributed through the of importance to investigate the dominant reasons Kamo River. The water front is a famous why the discharge of the Kamo River has been sightseeing place for local inhabitants and tourists. decreasing for river basin management. The variations of the Kamo River discharge have Hydrological dynamics are complex processes significant impact on the water-related landscapes. affected by various factors like climatic change, 1)-4) Modern water management in Kyoto has begun land use change and water management . Öztürk 5) about hundreds of years ago. Most notably, Lake et al. reported that the water budget was most Biwa canal, a waterway to transport water from sensitive to variations in precipitation in the Bartin 6) Lake Biwa to Kyoto city, has also more than 100 spring watershed, Turkey. Zheng et al. found that years’ history. The water from Lake Biwa is used land use played a dominant role followed by climate for potable water and the left water flows through change in reducing streamflow in the headwater 7) Kamo River Canal into the Kamo River and the Uji catchments of the Yellow River basin. Hu et al. River. According to an observation record at investigated that surface water resources were more Fukakusa station at the downstream of the Kamo sensitive to climate fluctuation than land use River basin, the river streamflow shows a changes in the middle reaches of the Yellow River. decreasing trend (Fig. 1). For keeping the natural However, the studies on the integrated impact of climate change and water management are still limited. In addition, the responses to climate change are high regional-dependence8). In the Kamo River basin, to date, there has been limited research on discharge variation9). Therefore, it is necessary to investigate to what degree water discharge has been altered by climate change and water management. The objectives of this study are to investigate the dominant reasons for the streamflow reduction of the Kamo River and to assess the relative contributions of precipitation, evapotranspiration and water management to the changes of streamflow. This study builds up our previous study9) by analyzing the impact of water resource management and separating the effects of each factor, and also use more observed data to improve the performance of model simulations.

2. STUDY AREA AND DATA

The area of this study is the upstream of Fukakusa station in the Kamo River basin (KRB), with a total area of 180 km2. The data used in this study is listed in Table 1, including meteorological data, water resource management related data and geographical data. The water management related data obtained from Kyoto City Waterworks Bureau (KCWB) includes total water intake from Lake Fig. 2 Study area and Lake Biwa canal Biwa canal (Fig. 1), water intake to all waterworks, water usage at the KRB, water into urban sewerage Table 1 Input data characteristics system and drainage area of sewerage system. The drainage area of sewerage system in Kyoto Data type Station Period Note 2 2 increased from 17.33 km in 1962 to 82.99 km in Precipitation Kyoto 1901-2014 Hourly 2014. Rainfall from 6 gauged stations (Fig. 2) are Temperature Kyoto 1901-2014 Hourly used and basin average precipitation is calculated (Fig. 1). Wind speed Kyoto 1943-2014 Daily Humidity Kyoto 1961-2014 Daily mm/year Sunshine duration Kyoto 1961-2014 Daily 6000 Precipitation Hieizan 1989-2000 Hourly Precipitation Kumogahata 1942-2014 Daily 5000 Precipitation Hanasetouge 1976-2009 Hourly

4000 Precipitation Hiei 2008-2014 Hourly Precipitation Hirokawara 1965-2014 Hourly 3000 River discharge Fukakusa 1962-2010 Daily Water from Lake 2000 - 1954-2014 Monthly Biwa Water intake to 1000 - 1954-2014 Monthly y = -16.214(x-1962) + 1723.8, p<0.05 Waterworks Water usage - 1962-2014 Monthly 0 Water into urban 1960 1970 1980 1990 2000 2010 - 1954-2014 Monthly Basin average precipitation sewerage system Lake Biwa canal Drainage area - 1962-2014 Annual Streamflow at Fukakusa station Land use - 2006 - Linear (Streamflow at Fukakusa station) DEM, Soil type - - Fig. 1 Annual statistics of observed data from 1962 to 2010 and River channel

3. METHODS climatic variability and human activities. By assuming their impacts are independent each other, (1) Water balance analysis the following relationship is derived: To separate the effects of water management, we = + (3) first estimate “natural discharge” (QN) by excluding in which △ QO is the total change in river △ 𝑄𝑄𝑂𝑂 △ 𝑄𝑄𝐶𝐶 △ 𝑄𝑄𝐻𝐻 the impact of water management from observed discharge, △QC is the change caused by climatic discharge at Fukakusa station (QO). For the KRB, variability (i.e. precipitation and temperature in this the water input includes precipitation and water study) and △QH is the change caused by human from Lake Biwa (VB). The water output contains activities (i.e. water management in this study). evapotranspiration, river discharge at Fukakusa △QO can be estimated from observed records. Thus, station (QO), water into all water supply systems if △QC or △QH is calculated, the contribution taking (VS), water through Kamo River Cancal into the Uji River (V ) and rainwater by sewerage ratio of each impact factor can be estimated. The C △ drainage system to the downstream of Fukakusa quantification of QC is described in Section 3 (4). station (VR). Thus, the water balance equation is as follows: (4) Hydrological modeling = + The Hydrological Predictions for the (1) 14), 15) Since the volume of rainwater directly flowing Environment model (HYPE) is used to 𝑂𝑂 𝑁𝑁 𝐵𝐵 𝑆𝑆 𝐶𝐶 𝑅𝑅 into sewage𝑄𝑄 (VR𝑄𝑄) is not𝑉𝑉 recorded,− 𝑉𝑉 − 𝑉𝑉 we− 𝑉𝑉estimate VR as investigate the river discharge change by the changes in precipitation and evapotranspiration. total water into sewage system (VDK) minus water 9) use in the basin (VSK) by assuming all the water use Compared with our previous application , the flows into the sewage system. Thus, the natural estimation method of potential evapotranspiration has been improved. In the previous study, a simple discharge at Fukakusa station (QN) can be calculated 16) as follows: function introduced in HYPE model manual was = ( + ) used with only temperature as a variable. Instead, (2) 17) Because the daily values of (VB – VS – VC – VDK this study applied Penman-Monteith method 𝑁𝑁 𝑂𝑂 𝐵𝐵 𝑆𝑆 𝐶𝐶 𝐷𝐷𝐷𝐷 𝑆𝑆𝑆𝑆 + VSK𝑄𝑄) cannot𝑄𝑄 −be𝑉𝑉 obtained,− 𝑉𝑉 − 𝑉𝑉the− 𝑉𝑉annual𝑉𝑉 values are which considers several climatic variables (i.e. equally divided into each day to estimate the daily wind, temperature, sunshine duration and humidity natural discharge for each year. Meanwhile, as in this study). In this simulation, the KRB was shown in Fig. 1 the observed discharge shows divided into 25 sub-basins and the precipitation of unrealistic high values between 1978 and 1987. each sub-basin is taken from the nearest rainfall Thus, the estimated natural discharge from 1989 to station. The model is calibrated from the initial 2010 is used for the model calibration and validation ranges of parameters values. The ranges are set manually based on hydrological knowledge and due to higher reliability in the recent record. In 16) addition, since there is no record of the volume of literature values . Based on a simple Monte Carlo water flowing through Kamo River Canal to the Uji simulation, with random 100,000 sets, the sample River (VC), the value of natural discharge (QN) is with the best performance is selected as a calibrated estimated on the assumption that all the water from parameter set. The performance is evaluated by Lake Biwa (VB) is used by water treatment plant (VS) Nash-Sutcliff efficiency (NSE) and Pearson and flows through Kamo River Canal to the Uji Correlation Coefficient (CC) between observations River (VC). The adequacy of this assumption will be and simulations. The change in streamflow due to discussed in Section 4. climatic variability (△QC) can be estimated from simulated streamflow. (2) Trend test In this study, Mann-Kendall test (MKT) is used 4. RESULTS AND DISCUSSION to detect the trends in hydro-climatic data10), 11). In addition, Sen’s Slope estimator procedure12), 13) is (1) Calibration and validation applied to estimate the slope of MKT analysis and The model was calibrated with the estimated determine magnitude of trends in hydro-climatic daily natural discharge from 2001 to 2010 and data. To match the observed discharge data period, validated from 1991 to 2000. The comparison of the trend tests of all hydro-climatic variables are simulated and natural daily streamflow is shown in conducted from 1962 to 2010. Fig. 3. The values of NSE and CC are 0.82 and 0.91 in the calibration period, and they are 0.79 and 0.90 (3) Contributions of climatic variability and in the validation period, respectively. Although the water management model tends to under estimate peak flows, it The changes of river discharge are induced by represents long-term natural discharge with the

reasonable values (NSE≈0.8 and CC≈0.9). Table 2. As there were some data missing of precipitation at some gauged stations, only trends of Calibration Period (2001-2010) precipitation at Kyoto station, Kumogahata station 400 0 and Hirokawara were analyzed. In addition, the trend of basin average precipitation was calculated. 100 There was a significant increase in temperature and

300 ) -1

s evapotranspiration (Fig. 4a and b). For 3 observed 200 precipitation, there was no statistical significance at simulated 200 the level of p = 0.05. Except for Kyoto station precipitation 300 showing a decreasing trend, all other stations

Discharge (m Discharge including the basin average precipitation show 100 400 increasing trends but not statistically significant. For natural discharge, there was a slight increase from 0 500 1962 to 2010 without statistical significance (Fig. 1/1/01 1/1/03 12/31/04 12/31/06 12/30/08 12/30/10 4b). According to the results of trend analysis, there Time are no similar changes and patterns in observed Validation Period (1991-2000) 400 0 streamflow and natural streamflow. Thus, the significant decrease in observed streamflow is not 100 mainly caused by climatic changes. In addition, the 300 ) ) Precipitation (mm) Precipitation changes in evapotranspiration are highly related to -1 s 3 observed 200 changes in temperature because of the similarities in simulated 200 patterns and trends in evapotranspiration and precipitation 300 temperature.

Discharge (m Discharge 100 25 ℃/year 400 (a) y = 0.021(x-1962) + 20.1, p<0.05

0 500 20 1/1/91 12/31/92 12/31/94 12/30/96 12/30/98 12/29/00 y = 0.03(x-1962) + 15, p<0.05 Time 15 Fig. 3 Comparison of simulated and natural daily streamflow at the KRB outlet 10 y = 0.037(x-1962) + 10.5, p<0.05

Table 2 Results of trend analysis on hydro-climatic data 5 Air temperature Maximum temperature Minimum temperature Year Z Sen’s Slope 0 1962 1968 1974 1980 1986 1992 1998 2004 2010 Air Temperature 5.08 Y 0.03 Max Temperature 3.49 Y 0.021 2500 mm/year (b) Mini Temperature 5.84 Y 0.037 2000 y = 5.782(x-1962) + 1616.2, p>0.05 Rainfall at Kyoto -1.04 N -3.093

Rainfall at Kumogahata 1.78 N 8.55 1500 Rainfall at Hirokawara 0.3 N 1.6 y = 1.902(x-1962) + 1074.2, p>0.05 Basin Rainfall 1.75 N 5.782 1000

Natural Discharge 0.66 N 1.902 y = 1.465(x-1962) + 756.9, p<0.05 500 Evapotranspiration 4.35 Y 1.465 Basin precipitation Evaptranspiration Natural discharge Observed Discharge -3.14 Y -16.214 Year 0 Z are statistics from MKT; Y means significant at the level of 1962 1968 1974 1980 1986 1992 1998 2004 2010 p=0.05. Fig. 4 Annual values of (a) temperature variables, (b) basin (2) Trend analysis precipitation, evapotranspiration and natural discharge The results of trend analysis from 1962 to 2010 for annual precipitation, temperature, simulated (3) Contribution analysis evapotranspiration and discharge are shown in Since the observed discharge shows unrealistic

high values between 1978 and 1987 (Fig. 1), in this In this study, the impact of land use is not study the first 15 years (1962-1976) and last 15 estimated. This is because the conversion between years (1996-2010) of the period 1962-2010 were land uses is small by comparing the land use data of selected to estimate the variations in hydro-climatic 1976 and 200618). In addition, the assumption that variables. Table 3 and Fig. 5 show the annual all the water from Lake Biwa (VB) is either used by average water balance components in millimeter for water treatment plant (VS) or flows through Kamo the periods 1962-1976 and 1996-2010. We decided River Canal (VC) in the period of 1989-2010 was to plot on different directions according to in (+) or tested based on water balance analysis. The results out (-) for water balance in the KRB. It was found showed that there was less than 100 mm per year that the annual mean basin average precipitation, flows from Lake Biwa canal to the Kamo River in evapotranspiration and natural streamflow of the this period, which was about 3% of the total water KRB in the period 1996 to 2010 were about 161.4 per year from Lake Biwa canal. Thus, the mm, 35.4 mm and 28.8 mm more than that of the assumption is reasonable since the bias induced by period 1962-1976, respectively. Climate variability the assumption is not large. resulted in a slight increase in streamflow due to the increase of precipitation. However, in observed discharge, there was a decrease of 470.1 mm from QO the period 1962-1976 to the period 1996-2010. The VR VC primarily reasons are the variations of water intake V 1996-2010 S from Lake Biwa canal to the Kamo River and the VB increase of drainage areas of sewer system. It was QN E found that water from Lake Biwa (VB) of the period P 1996-2010 was about 115.1 mm less than that of the period 1962-1976 whereas water into watertakes QO

(VS) increased 304.6 mm. And water through Kamo VR V River Cancal into the Uji River (VC) decreased by C V 80.0 mm. Thus, the water intake from Lake Biwa to 1962-1976 S the Kamo River (V – V – V ) had a reduction of VB B S C QN

335.7 mm. Meanwhile, rainwater through sewerage E P system to the downstream (VR) increased by 163.2 mm/year mm due to the increase of the drainage area of sewerage systems. In total, there was a decrease of -2000 -1000 0 1000 2000 3000 4000 Qo VR 498.9 mm in annual average river discharge due to Vc Vs the impact of water management. The contribution VB QN Evapotranspiration (E) Basin precipitation (P) radios of climate variability and water management to the reduction of river discharge from the period Fig. 5 Water balance components in the KRB for the periods 1962-1987 to the period 1989 to 2010 are about 1962-1976 and 1996-2010 (Minus value represents water going -6.1% and 106.1% (71.4% induced by the change in out from the basin) Lake Biwa canal and 34.7% induced by sewage system, Table 4). Table 4 The contribution radios of different factors to river discharge change Table 3 Water balance components in the KRB for the periods Variations Contribution to

1962-1976 and 1996-2010 (mm/year) discharge reduction (%) 1962- 1996- Total change -470.1 100 Unit: mm Change 1976 2010 Change by climate 28.8 -6.1 Basin precipitation (P) 1631.3 1792.7 161.4 variability Evapotranspiration (E) 630.1 665.5 35.4 Change in Lake -335.7 71.4 Natural discharge (QN) 1084.1 1112.9 28.8 Biwa canal Water from Lake Biwa (V ) 3297.2 3182.1 -115.1 Change by sewage B -163.2 34.7 water into watertakes (VS) 1013.5 1318.1 304.6 drainage system Water through Kamo River Cancal into the Uji River 1854.4 1770.4 -80.0 5. CONCLUSION (VC) Rainwater through sewerage system to the downstream 45.7 208.9 163.2 The Kamo River can be regarded as the cultural (VR) source of Kyoto-city, Japanese historical capital. Observed discharge (QO) 1467.6 997.5 470.1 Because of climate variability and human activities,

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