IMPACT OF CLIMATE VARIABILITY ON CROP WATER REQUIREMENT - A DETAILED STUDY FOR THE STATE OF KARNATAKA

Abstract

Climate variability is the distribution of weather patterns over periods ranging from seasons to several years (below normal), while climate change is the changes in the distribution of weather patterns over periods ranging from decades to millions of years. In the recent decades, global agriculture has threatened by climate change and climate variability, and it is one of the important challenges to increase food production for the rapidly growing population under increased stress environment. So it is necessary to study the climate variability and its impacts on agricultural water resources to achieve the stable and sustainable crop-water management and - minimize its effects. The present study is carried out to study the statistical analysis of precipitation and temperature along with study of abnormal wetness and dryness over 28 districts of the state of Karnataka, India. In addition, a proposed design of crop water requirement (CWR) using CROPWAT model was suggested incorporating climate variability. Statistical trend analysis techniques, namely the Mann—Kendall test and Theil-Sen's slope estimator test, were used to examine trends in both parameters at the 5% level of significance. For all the analysis (objectives), investigation was carried out at different interval of periods to better understand the fluctuation of precipitation and temperature from the normal value. Similar time periods were studied for variation in CWR due to changes of climate parameters such as wind speed, sunshine hour, relative humidity, temperature and precipitation. Data analysis showed that from the period of 1901-1980 there was no trend in all seasons - as well as annual mean for precipitation and mean temperature at 5% significance level in the study area. During the last 113 years (1901 -2012) increasing trend in precipitation observed in north cast districts (also in Bangalore urban district) of Karnataka, while decreasing trend was found in the districts under transition zone. The magnitude of increasing trend in annual precipitation varied from 90.4 to 150.3 mm in the last Il 3 years. The mean temperature increased by 0.60, 0.22, 0.67, 0.46 and 0.31°C for the pre-monsoon, monsoon, post-monsoon, winter and annual mean temperature respectively over the past 102 years in the study area. Magnitude of trend variation is dominant in monsoon season and annual mean for precipitation, iv S while pre-monsoon and winter seasons are the dominant seasons for mean temperature. In addition, the increasing trend for annual mean temperature increases with latitude (12.9702° N to 77.5603° E) in the study area. But for the seasonal basis, severity of increase in trend of temperature is varying with seasons. For the study area standard precipitation index (SPI) values range from + 3.02 to - 3.05 indicating variation in precipitation over the period of 1950-2012. Further, district-wise SPI maps showed during 2001 to 2012 there is a considerable change in number of dry and wet years occurred. The number of dry years is increased in the districts under transition zone in the last twelve years (eg., Belgaum, Dharwad, Haven etc). While during the same period for the districts - under north east dry zone and Western —Ghats the number of wet years are increased. Analysis of CWR is carried out at agro-climatic zone wise i.e. one district is selected for each zone for detailed analysis. Subsequently for calculating CWR two periods of climate parameters (monthly wind speed, sunshine hour, relative humidity, minimum and maximum temperature) average were taken i.e. 1971 - 2000 and 2001 - 2012. Analysis of water requirement of cotton, groundnut, maize and wheat crops showed that there is significant impact of climate variability in the study area; however it is heterogeneous in nature. In the Northern dry zone, there is strong negative effect of climate variability on CWR, consequently in the Northern transition zone and Southern dry zones. The effect of climate variability is dominant for the Kharif season as compared to Rabi season in these zones (except for wheat crop in the Northern transition zone). The climate variability has positive effect in terms of CWR on four zones of study area such as Eastern dry zone, North eastern transition zone, Central dry zone and North eastern dry zone. 1-lowever for the Coastal and hilly zones there is no effect of climate variability on CWR (except for wheat crop).