Climate change projections for Tamil Nadu, India: deriving high-resolution climate data by a downscaling approach using PRECIS Prasanta Kumar Bal, A. Ramachandran, R. Geetha, B. Bhaskaran, P. Thirumurugan, J. Indumathi & N. Jayanthi Theoretical and Applied Climatology ISSN 0177-798X Theor Appl Climatol DOI 10.1007/s00704-014-1367-9 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Theor Appl Climatol DOI 10.1007/s00704-014-1367-9 ORIGINAL PAPER Climate change projections for Tamil Nadu, India: deriving high-resolution climate data by a downscaling approach using PRECIS Prasanta Kumar Bal & A. Ramachandran & R. Geetha & B. Bhaskaran & P. Thirumurugan & J. Indumathi & N. Jayanthi Received: 13 November 2013 /Accepted: 30 December 2014 # Springer-Verlag Wien 2015 Abstract In this paper, we present regional climate change significant exceptions are noticed over some pockets of west- projections for the Tamil Nadu state of India, simulated by the ern hilly areas and high rainfall areas where increases in rain- Met Office Hadley Centre regional climate model. The model fall are seen. There are also indications of increasing heavy is run at 25 km horizontal resolution driven by lateral bound- rainfall events during the northeast monsoon season and a ary conditions generated by a perturbed physical ensemble of slight decrease during the southwest monsoon season. Such 17 simulations produced by a version of Hadley Centre an approach of using climate models may maximize the utility coupled climate model, known as HadCM3Q under A1B sce- of high-resolution climate change information for impact- nario. The large scale features of these 17 simulations were adaptation-vulnerability assessments. evaluated for the target region to choose lateral boundary con- ditions from six members that represent a range of climate variations over the study region. The regional climate, known as PRECIS, was then run 130 years from 1970. The analyses 1 Introduction primarily focus on maximum and minimum temperatures and rainfall over the region. For the Tamil Nadu as a whole, the The Intergovernmental Panel on Climate Change (IPCC) pro- projections of maximum temperature show an increase of 1.0, jects a rise in global average surface temperatures between 1.1 2.2 and 3.1 °C for the periods 2020s (2005–2035), 2050s and 2.9 °C by 2100 for a low-emission scenario and between (2035–2065) and 2080s (2065–2095), respectively, with re- 2.4 and 6.4 °C by 2100 for a high-emission scenario in its spect to baseline period (1970–2000). Similarly, the projec- fourth assessment report (IPCC 2007). The report by IPCC tions of minimum temperature show an increase of 1.1, 2.4 (2012) indicates that it is likely that the frequency of heavy and 3.5 °C, respectively. This increasing trend is statistically precipitation events will increase in the 21st century over significant (Mann-Kendall trend test). The annual rainfall pro- many areas of the globe. The expected impacts of climate jections for the same periods indicate a general decrease in change and the global warming range from changing rainfall rainfall of about 2–7, 1–4and4–9 %, respectively. However, pattern to increased salinity of the soil, lack of availability of potable water, inundation of coastal areas by sea water, etc. P. K. Bal (*) : A. Ramachandran : R. Geetha : P. Thirumurugan : The major factor which causes concern is the steady increase N. Jayanthi in temperature and variability in rainfall pattern owing to cli- Centre for Climate Change and Adaptation Research, Anna mate change. Though climate change is a long-term phenom- University, Chennai 600025, India enon, its effect could be slowly and steadily creeping in im- e-mail: [email protected] perceptibly. Hence, it is very important to develop and plan : : P. K. Bal R. Geetha J. Indumathi mitigation and adaptive strategies to address these issues. Ad- Department of Information Science and Technology, Anna vances in climate change modelling now enable best estimates University, Chennai 600025, Tamil Nadu, India and likely assessed uncertainty ranges for projected warming B. Bhaskaran for different emission scenarios as per IPCC (2007). The Fujitsu Laboratories of Europe, Middlesex, UK coarse horizontal resolution global climate models (GCMs) Author's personal copy P.K.Baletal. have limitations in capturing the regional orographic features, been carried out for Tamil Nadu using RCMs with multiple whereas the high-resolution regional climate models (RCMs) ensemble members with a resolution of 25 km to assess cli- represent the orography better and hence are capable of pro- mate change and its uncertainty. There is particularly an ducing more realistic precipitation climatologies (Kumar et al. emerging need to produce high-resolution climate change in- 2013). RCMs are limited area models and therefore need to be formation with its uncertainty range for a few key climate driven by time-dependent large-scale fields (e.g. wind, tem- variables for Tamil Nadu state to enable adaptation options perature, water vapour, surface pressure, and sea-surface tem- for the water, agriculture, and manufacturing sectors. This is perature (SST) at model sea grid-boxes) at their boundaries; the first ever study for this region that utilizes six-member this information is provided by a version of the Hadley Centre transient regional climate model simulations at 25 km hori- GCM, HadCM3 (Gordon et al. 2000; Collins et al. 2001). zontal resolution to project changes in key climate parameters HadCM3 was one of the major models used in the IPCC Third and the associated uncertainty. Climate variability and climate and Fourth Assessments and also contributes to the Fifth As- change projections for the climate parameters maximum tem- sessment. It is a coupled climate model that has been used perature (max. temp.), minimum temperature (min. temp.), extensively for climate prediction and other climate sensitivity and rainfall at both the long-term annual and seasonal scales studies. The Providing Regional Climates for Impacts Studies over the entire Tamil Nadu with agro-climatic zone (ACZ) (PRECIS), the third-generation Hadley Centre RCM is based wise distributions is attempted in this paper. on the atmospheric component of HadCM3 with substantial modifications to the model physics. Several studies have em- 1.1 Current climatology over Tamil Nadu phasized on regional climate modelling systems to quantify the uncertainty of the projected climate change at a regional The climate of Tamil Nadu is mainly of tropical semiarid type. scales with a coarse resolution (≈50 km) version of the The geographical location of Tamil Nadu makes it as one of PRECIS (Mohammad and Md 2012; Jones et al. 2012;Met the most vulnerable maritime states in India particularly to Office Report 2012). tropical cyclones and their associated storm surges. It is fre- PRECIS simulation for Bangladesh shows a good perfor- quently subjected to extreme weather conditions of flooding mance while calibrating temperature and rainfall for the re- in coastal districts and severe droughts chronically in some gion. It was found to produce successful seasonal forecasting areas and periodically in others. The temperature in summer of meteorological parameters like rainfall and temperature for seldom rises above 45 °C and in winter seldom falls below Bangladesh (CCC 2009;NazrulIslam2009; Mohammad 18 °C. Temperatures and humidity remain relatively high all et al. 2012). State level adaptation studies in India also have year round. Tamil Nadu gets rainfall from the northeast (NE) been done for Madhya Pradesh and Odisha using model out- and southwest (SW) monsoon seasons. As per the SoE report puts from PRECIS generated by IITM, Pune (Synthesis Re- (2005) of Tamil Nadu, the normal rainfall in the state is about port 2012; Final Report 2012). Rupakumar simulated the re- 950 mm with an average number of 50 rainy days. Being gional climate of India by using PRECIS model for the base- located on the leeward side of the Western Ghats, it gets only line (1961–1990) as well as for the end of the century (2071– about 32 % of the annual rainfall during the SW monsoon 2100) for A2 and B2 SRES scenarios (Rupa Kumar et al. season (June–September). During the NE monsoon, the prin- 2006). Krishnakumar used PRECIS to simulate the regional cipal rainy season (October–December), it receives about climatology of India for SRES scenario A1B (Krishna Kumar 48 % of the annual total rainfall (Balachandran et al. 2006; et al. 2011). Several PRECIS-based RCM applications on Selvaraj and Rajalakshmi 2011; Indira and Stephen Rajkumar subregional scales were carried out by various studies in India Inbanathan 2013). The rainfall in this season is highly variable (Bhaskaran et al. 1996; Bhaskaran et al. 2012a; b;Kulkarni due to its cyclonic nature. Tamil Nadu is divided into seven et al. 2013). The analyses from many CMIP3 GCMs over agro-climatic zones: northeastern, northwestern, Cauvery del- south Asia show that only six GCMs out of 18 are able to ta, western, high-altitude, southern and high rainfall zones. capture the precipitation pattern between models and observed The total area covering each zone with districtwise distribu- precipitation with a relatively small root mean square differ- tion is given in Table 1.