Assessment of Evapotranspiration Rates and Water Deficit in Kaduna State

Evapotranspiration (ET) represents the dominant component of the water balance in most Nigerian ecological zones and is a critical parameter for irrigation scheduling and water resource management. This study assesses reference evapotranspiration (ETo) rates and seasonal water deficits in Kaduna State using the FAO Penman-Monteith method applied to daily meteorological data from NiMet stations in Kaduna and Kafanchan covering 2018 to 2022. Climatic water deficit, defined as the difference between potential evapotranspiration and actual rainfall, was computed on a monthly basis and mapped to agricultural cropping calendars for dominant crops including maize, sorghum, and groundnuts. Results indicate that Kaduna State experiences pronounced water deficits between October and April, with cumulative dry-season deficits exceeding 800 millimetres in the northern sections of the state. The growing season deficit for groundnuts, calculated as the difference between crop water requirement and effective rainfall, averages 120 millimetres, indicating a need for supplemental irrigation. Comparison of ETo estimates from Penman-Monteith with simpler Hargreaves-Samani estimates reveals acceptable agreement (r-squared = 0.88) under data-scarce conditions, suggesting that the simpler method may serve as a practical substitute. Recommendations include establishment of supplemental irrigation infrastructure in deficit-prone LGAs and training of agricultural extension workers in ET-based irrigation advisory. Keywords: evapotranspiration, water deficit, Kaduna, Penman-Monteith, irrigation.