ANALYSIS OF SPATIOTEMPORAL PATTERNS AND TRENDS OF CLIMATE VARIABILITY AND ITS PERCIEVED IMPACTS ON LAKE HAWASSA WATERSHED

ABSTRACT Climate change is largely indicated by the spatiotemporal patterns and trends of rainfall and temperature. To this end, this study analyzes spatiotemporal patterns and trends of climate variability and its perceived impacts on Lake Hawassa Watershed in the Central Rift Valley of Ethiopia by using a mixed research methods. The study used gridded longitudinal temperature and rainfall data at a resolution of 4*4 km for the period 1984-2020 to analyze spatiotemporal patterns, trends of climate change, and drought incidents. Systematically randomized 177 households were surveyed on perceptions about trends of climate variability to triangulate the results of long-term temperature and rainfall data and to collect perceived impacts of climate change. For data processing and analysis, software packages such as XLSTAT 2020, ArcGIS 10.5 and SPSS were used. Non-parametric Mann-Kendall trend test was employed as a tool to see whether there has been statistically significant decreasing or increasing temporal trends, while Sen’s slope estimator was used to calculate the rate of change of variability in rainfall and temperature at 5% level of significance. To analyze spatial patterns and map areal dispersion of rainfall and temperature in the study area, ordinary kriging was applied. On the other hand, Standardized Rainfall Anomaly (SRA) was applied as a tool to calculate drought incidents based on rainfall data (1984 2020). On annual and decadal scales, the results from Mann-Kendall trend tests (S=-44, -0.66 and Z=-0.846) at 5% level of significance and Sen’s slope estimator have indicated that the rainfall showed statistically insignificant decreasing trend with average decreasing rate of -1.51 mm (p-value=0.397); while the minimum and maximum temperatures showed statistically significant increasing trends at 5% level (S=464, 421; 0.697, 0.633; Z= 18.35, 10.35; p-value<0.001, <0.0001) with average increasing rate of 0.0830C and 0.0790C, respectively. On spatial scale, the result of spatial patterns of mean annual rainfall has showed that the amounts of rainfall in the study area increased from the north at Toga hills to the south at Gorche-Shamana rugged hills ranging from 760.90 mm to 1,397.24 mm, respectively. Unlikely to rainfall, the results of spatial patterns of temperature have indicated that the temperature in Lake Hawassa Watershed increased from the west at Shamana-Bake Lalima rugged hills and the east at parts of Wondo Genet and Gorche rugged hills to the central north at Shashamane-Hawassa flat areas with 8.180C-13.740C minimum and 20.430C-27.350C maximum temperatures, respectively. The results from annual SRA have indicated that the study area had experienced nine years (1984, 1990, 1999, 2000, 2003, 2009, 2012, 2015, and 2018) of drought incidents with different extents and twenty eight years with no droughts. On the other hand, the result of perceived trends of climate variability in the study area indicated that 94.9% and 99.43% of households perceived that rainfall and temperature in the study area showed decrease and increase, respectively. This further implies that, the result supports decreasing rainfall and increasing temperature trends from long-term metrological records (1984-2020). Additionally, the perceived result showed that the study area has experienced the impacts of climate variability such as drought, flooding, loss of agricultural production, and destruction of infrastructure. Therefore, the study area had been experiencing the decreasing rainfall and increasing temperature trends on the temporal scale. Besides, the study area had been receiving the higher amounts of rainfall in the southern and the lower in the northern parts; while the temperature increases from the west and east towards the central north. Generally, the rainfall and temperature show temporal and spatial variability with associated impacts of climate change in the study area. Thus, study suggests that the concerned body should be taken measures towards developing integrated Lake Watershed natural land cover and anthropogenic land use policy strategies in order to keep the balance of energy exchanges between land surface and atmosphere to regulate trends of variability in rainfall and temperature and associated impacts.