Impact of projected climate change on cropping pattern of different agro ecological units of Central Kerala

Abstract

Agriculture faces hastily growing challenges because it must supply food to an increasing population under shifting climate conditions. To stabilize the negative effects of climate change, researchers have generally emphasized incremental adaptation to existing cropping systems, such as the adjustment of planting window, suitable variety and improved agronomic practices. Characterization of the ecosystems using the AEZ concept is a good decision making approach for variety of farming activities performed by the farmers and is a useful tool for the studying the impact of climate change. The objectives of this study are (1) To study rainfall variability and to determine water availability periods of Agro ecological units of Central Kerala under different climate change scenarios. (2) To study the impact of projected climate change on cropping pattern, crop calendar and the possible changes in the water requirements of major cropping systems prevailed in the various Agro ecological Units of central Kerala. Daily rainfall data for the period 1991-2014 were collected from the India Meteorological Department, Thiruvananthapurm. The weather data from General Circulation Models based on RCP 4.5 and 8.5 were analyzed. Weather cock v.1.5 was used for converting the daily weather data into standard week, month and seasonal formats. The rainfall parameters or indices like seasonal and monthly rainfall, rainy days, high rainfall events, length of growing period were calculated. It is also used to compute PET and Thornthwaite water balances. CROPWAT model was used for the calculations of crop evapotranspiration, crop water requirements and irrigation requirements for the development of irrigation schedules under various management conditions and scheme water supply. A decline in rainfall can be observed during the months January, February, September and December in projected climate as per RCP 4.5 and 8.5 whereas an increased rainfall during the months June, July and August. In nut shell the wet months will be wetter and dry periods will be drier. The south west monsoon and summer season shows an increasing trend in the number of rainy days and amount of rainfall in projected climate. The projected climate indicates that there will be a decreasing trend in the number of rainfall events below 50 mm per day whereas the heavy rainfall events show an increasing trend. Most of the agro ecological units in central Kerala indicate a decreasing pattern in the length of growing period in projected climate as per RCP 4.5 and 8.5. In projected climate the maximum amount of potential evapotranspiration can be observed during the months May, July and September whereas the minimum will be in January, November and December. The number of periods were deficit will happen indicate an increasing trend and also the annual amount of deficit show an increasing pattern in projected climate. A shift in the water surplus periods can be observed during projected climate. Most of the AEUs in central Kerala indicate a reduced number of surplus periods in projected climate. The crop evapotranspiration indicate an increasing trend in the rice based cropping system during the projected climate whereas in perennial crops it shows a decreasing trend. The water requirement indicates an increasing trend in most of the major cropping systems whereas in Rice-Fallow-Fallow cropping the irrigation requirement remains unchanged. As a general trend, the length of growing period in the major rice growing areas of different AEUs are getting shorter with slight differences among various agro-ecological units, implying a higher risk of operating under projected climate as per RCP 4.5. The crop calendar of rice based cropping system indicates a delay in sowing date due to delay in summer showers and the crops will have to suffer water stress during the grain filling stage and will be under heavy rains at the time of harvest in projected climate as per RCP 4.5.