Crop water requirements of crops in agro-ecological units (AEUs) of Palakkad district of humid tropical Kerala computed with CROPWAT 8.0 using the meteorological parameters.The major cultivated crops are rice, coconut, banana, arecanut, vegetables, pulses, rubber, tea, coffee, cotton etc. The total water requirement for these crops in various agro-ecological zones has been computed. Using the evapotranspiration (ET 0 ) and effective rainfall in each agro-ecological unit (AEU), a climatic water balance has been worked out. The net irrigation demand, the gross irrigation demand and irrigation interval for the various crops grown in different AEUs have been computed. The gross irrigation demand for the district is 1146 Mm 3 , in which 981 Mm 3 is from surface water and 165 Mm 3 from groundwater sources. Water balance analysis was done for the current scenario and future demand for agriculture, domestic and industrial demand. The projected future total water demands for irrigation, drinking and industrial purpose will be 3841 Mm 3 . However, the secondary data showed that utilizable water resources of Palakkad district is less and will create a deficit scenario. This deficit indicates that if the total area is brought under irrigation there will be deficit years and during such periods deficit irrigation or reduction in command area may have to be adopted. A wide spectrum of scenarios has been discussed in the paper along with the guidelines for future management of water resources.

Rise in temperature is one of the predicted impacts of climate change with significant implications on water resources management. An attempt has been made to calculate the water requirement of crops in different agro-ecological zones of Palakkad district in humid tropical Kerala using the CROPWAT 8.0 model. Sensitivity analysis was done for a simulated rise in temperature from 0.5 to 3.0 °C keeping other parameters the same. The analysis showed that the total crop water requirement of all the major crops, like coconut, paddy and banana, increased with rising temperature thereby increasing the simulated irrigation water demand. The gross water demand inclusive of irrigation, domestic and industries will be 1,496 Mm3. The simulated gross water demand for an increase in temperature of 0.5, 1.0, 2.0 and 3.0 °C will be 1,523, 1,791, 1,822 and 1,853 Mm3, respectively. The maximum utilizable water resource available in the district is only 1,579 Mm3 and better water management, focusing particularly on improving the irrigation efficiency, has to be adopted to cater for the demands of the user sectors under changing climate scenario. A wide spectrum of climate change scenarios is also discussed in the paper along with guidelines for the future management of water resources.

An effort has been made to calculate the water needs for various crops in different agro-ecological units (AEUs) of Kollam district (a humid tropical region of Kerala) using FAO-CROPWAT. The major cultivated crops are rice, coconut, rubber, pepper, banana, brinjal, tomato, tapioca, cardamom, tea, etc. The gross water required for these crops has been computed in various AEUs using meteorological parameters. Using evapotranspiration and effective rainfall in each unit, a water balance has been worked out. An overall water balance of the district has been attempted by considering irrigation, domestic and industrial demand of AEUs, under current scenario and future demand. The gross irrigation demand for the currently irrigated area in the district at 70% efficiency is 1045 mm 3 , of which 920 mm 3 is supplied from surface water sources and 125 mm 3 from groundwater sources. The projected future total water demands for irrigation, drinking and industrial purposes will be 2667 mm 3 . However, the utilizable water resource from all river basins of Kollam is only 1117 mm 3 . The above data shows a deficit of 1550 mm 3 and it will be difficult to arrive at requirements with the existing water resources at a given point of time. We infer that if the total area is brought under irrigation, there will be water scarce years, and hence decreasing irrigation or the command area needs to be adopted to manage this shortfall and sustain production. We have also discussed several options/strategies for better water management under these changing climatic circumstances to provide water to meet the demands of all the users.