Spatiotemporal climate and vegetation greenness changes and their nexus for Dhidhessa River Basin, Ethiopia

Background Understanding spatiotemporal climate and vegetation changes and their nexus is key for designing climate change adaptation strategies at a local scale. However, such a study is lacking in many basins of Ethiopia. The objectives of this study were (i) to analyze temperature, rainfall and vegetation greenness trends and (ii) determine the spatial relationship of climate variables and vegetation greenness, characterized using Normalized Difference in Vegetation Index (NDVI), for the Dhidhessa River Basin (DRB). Quality checked high spatial resolution satellite datasets were used for the study. Mann–Kendall test and Sen’s slope method were used for the trend analysis. The spatial relationship between climate change and NDVI was analyzed using geographically weighted regression (GWR) technique. Results According to the study, past and future climate trend analysis generally showed wetting and warming for the DRB where the degree of trends varies for the different time and spatial scales. A seasonal shift in rainfall was also observed for the basin. These findings informed that there will be a negative impact on rain-fed agriculture and water availability in the basin. Besides, NDVI trends analysis generally showed greening for most climatic zones for the annual and main rainy season timescales. However, no NDVI trends were observed in all timescales for cool sub-humid, tepid humid and warm humid climatic zones. The increasing NDVI trends could be attributed to agroforestry practices but do not necessarily indicate improved forest coverage for the basin. The change in NDVI was positively correlated to rainfall (r2 = 0.62) and negatively correlated to the minimum (r2 = 0.58) and maximum (r2 = 0.45) temperature. The study revealed a strong interaction between the climate variables and vegetation greenness for the basin that further influences the biophysical processes of the land surface like the hydrologic responses of a basin. Conclusion The study concluded that the trend in climate and vegetation greenness varies spatiotemporally for the DRB. Besides, the climate change and its strong relationship with vegetation greenness observed in this study will further affect the biophysical and environmental processes in the study area; mostly negatively on agricultural and water resource sectors. Thus, this study provides helpful information to device climate change adaptation strategies at a local scale

Hydrological analysis of the Upper Tiber River Basin, Central Italy: a watershed modelling approach

"Quantification of the various components of hydrological processes in a watershed remains a challenging topic as the hydrological system is altered by internal and external drivers. Watershed models have become essential tools to understand the behavior of a catchment under dynamic processes. In this study, a physically-based watershed model called Soil Water Assessment Tool (SWAT) was used to understand the hydrologic behavior of the Upper Tiber River Basin, central Italy. The model was successfully calibrated and validated using observed weather and flow data for the period of 1963–1970 and 1971–1978 respectively. Eighteen parameters were evaluated and the model showed high relative sensitivity to groundwater flow parameters than the surface flow parameters. Analysis of annual hydrological water balance was performed for the entire upper Tiber watershed and selected sub-basins. The overall behavior of the watershed was represented by three categories of parameters governing surface flow, sub-surface flow and the whole basin response. The base flow contribution has shown that 60% of the stream flow is from shallow aquifer in the sub-basins. The model evaluation statistics that evaluate the agreement between the simulated and observed streamflow at the outlet of a watershed and other three different sub-basins has shown coefficient of determination (R2) from 0.68 to 0.81 and Nash Sutcliffe Efficiency (ENS) between 0.51 and 0.8 for the validation period. The components of the hydrologic cycle showed variation for dry and wet period within the watershed for the same parameter sets. Based on the calibrated parameters the model can be used for prediction of the impact of climate and land use changes and water resources planning and management