The scarcity of water in semi-arid area of Kiboko, Makindu sub-county is a major contributor tolow maize yield beside climate change due to little and unreliable rainfall. Regulated deficit irrigation is a water management technique that improves water use efficiency to obtainminimal yield and irrigation cost benefit. An experiment was carried out for two seasons in Kiboko, Makindu Sub-County during 2018 and 2019 short and long rains, respectively to evaluate the response of maize growth and yield to regulated deficit irrigation in semi-arid area. The experiment was a Randomized Complete Block Design with three blocks replicated three times. The treatments were T1 (100% field capacity), T2 (75% field capacity, T3 (50% field capacity), T4 (25 % field capacity) and T5 (rain-fed) were evaluated. The highest maize yield obtained in season I was 10.9tha-1recorded under full irrigation (T1) followed by 10.4tha-1 obtained in T2, 9.8tha-1 obtained in T3 (50% field capacity), 9.0tha-1 in T4 and the lowest maize yield was 8.4tha-1recorded under rain-fed (T5) while in season II the highest maize yield of 10.2tha-1 was recorded in T1, followed by 9.1tha-1 in T2, 8.3tha-1 in T3, 6.0tha-1 in T4 and the lowest maize yield of 3.0tha-1 was obtained under rain-fed (T5).However,the highestwater use efficiency recorded in season I was22kgha-1mm-1 obtained under rain-fed(T5), 19.8 kgha-1mm-1 recorded in T3 (50% field capacity) while in season II the highest WUE of 24.8kgha-1 mm -1 was recorded in T3, followed by 23.7kgha1mm-1 in T2 and the lowest WUE was 16.6kgha-1mm-1 obtained under rain-fed (T5). Two climate change scenarios (2020-2039) and (2040-2059) were projected and modelled by global circulation model (GCM) and the yield was predicted usingAquaCrop water productivity model. The GCM indicated atemperature rise of1 0C which will affect the future rainfall patterns in the study area. The model predicted rainfall to increase by 15% in season I (short rains) and reduce by 10.1% in season II (long rains) compared to the baseline climate (1986 – 2005). The predicted yield of maize will remain constant under irrigation water management thoughit will significantly vary under rain-fed conditions due to temperature rise and rainfallvariation patterns which affect the crop water requirementat 401mm. The water management practices such as 100% soil surface cover will counteract the effect of climate change by reducing soil surface evaporation, net irrigation requirement and maintaining soil moisture and temperature.

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