Toward a Hydro-Economic Approach for Risk Assessment and Mitigation Planning of Water Disasters in Semi-Arid Kenya
Cush, Ngonzo Luwesi
Obando, Joy Apiyo
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The study objectives were to: (i) assess socio-economic and environmental externalities affecting efficient use of water and land resources in farming activities at Muooni dam site; (ii) determine the extent to which land use activities affect the active water storage capacity of Muooni dam; (iii) simulate the variations of farmers‟ water demand and related operational costs resulting from rainfall fluctuation in Muooni catchment; (iv) and estimate the farmers‟ water economic order quantity and limit average cost related to their production efficiency under fluctuating rainfall regimes. To achieve these goals, the following empirical tools were used: an on-farm field survey (involving 66 farmers) and off-farm in-depth interviews (of 60 key informants). Numerical tools of data analysis comprised descriptive, non-parametric and time series statistical analyses along with operational research simulations, utilizing SPSS and MS EXCEL spreadsheets and DOVIEW logic models. The study reveals that land-use activities assessed at Muooni dam site do not have a significant impact on its soil erosion and water over-abstraction (as attested by Mann-Witney U-test and Spearman‟s rank correlation with 99.8% confidence degree). However, the siltation of the dam reservoir may explain 61% of the total variation of the dam‟s active water storage capacity decrease (as certified by Spearman‟s Rho test with 99.5% confidence degree). This is mainly explained by off-site soil erosion impacts (due to external agents like El Niño floods and droughts, heavy winds pressure, footpaths and roadside erosion, sand harvesting and deforestation) and alien trees planting adverse effects on water. Rainfall fluctuation is the main controlling factor of land-use at Muooni dam site. Also, land management is highly correlated with farmers‟ education and poverty levels. Along with farmlands sub-division, it accelerates the risk of soil erosion and water excess loss in the catchment. These in turn increase water cost (through significant shortage costs) and affect farming yields and incomes. Farmers have therefore adopted multiple cropping of about 9 perennial crops and 6 seasonal species on small farmlands as a strategy for facing poor incomes, especially during unpredictable droughts. Yet, farmers cannot meet their actual crops water requirements. The operational research simulations reveal that LSF, MSF and SSF farmers are ordering respectively 29%, 12% and 4% of their respective actual crops water requirement. An increase of about 175%, 518% and 11,437% of their actual total costs is observed respectively under ANOR, NOR and BNOR scenarios. For efficiency, LSF, MSF and SSF farmers are urged to increase their respective actual water demand by an average of 148%, 142% and 152% to meet their water EOQ. By so doing, they could expect a fall of their operational costs up to 40%, 70% and 98% under the three respective scenarios. The study recommends that they limit their current average costs increase below 100 %, if the viability of their economic activities is to improve. They have also to limit their production under a MES ranging from 68% to 98% of their average costs, especially under NOR and BNOR scenarios, while their water demand variation is limited to 129% and 972% (instead of 518% and 11,437%). The differential rate has to be compensated either by rainfall input or better by hydropolitical strategies, efficient on-farm management techniques and technological innovation. The Government of Kenya was urged to put in place policy intervention measures that back farmers‟ initiatives within a CMS of the Athi Catchment and a SCMP of Muooni Sub-Catchment.