RESPONSES OF HYDROLOGICAL COMPONENTS TO LAND USE/LAND COVER CHANGE AND CLIMATE VARIABILITY

Abstract

Land use/ land cover (LULC) changes and climate variability have significantly affected Tanzania's water cycle over the years. Population development, climate change, and variability evolving new demands as a result of global growth and varying consumption habits have contributed to a decrease in fresh water supply and distribution over time. Water supplies will face critical challenges due to food and energy security, urbanization and industrial development, and climate change. Spatial and temporal changes greatly influence water supply in conservational fluctuations, climate and land use/cover diminuendos are two examples. The supply and demand sides of the equation could be affected by climate change and variability, adding to the difficulties. Land-cover changes are particularly noticeable in developing countries with promptly rising human populations and agriculture-based economies. The resulting increases in water supply and increased per capita water demand would harm those countries' food, water, and energy protection. As a result, assessing the catchment's response to environmental changes is essential for long-term water supply management and development in this critical part of the basin. Evaluating the contributions of changes in water balance components in individual LULC classes, in particular, is critical for successful control of water and land resources as well as climate change mitigation. Using SWAT model, this research aims to evaluate the effects of climate variability and land use/ land cover change on the hydrology of Kilombero sub-basin. The study looked at the hydrologic effects of climate and land use changes in three ways. These three ways are (i) analyzing the responses of hydrological components to only land use/land cover changes, (ii) assessing the responses of hydrological components to only climate variability, and (iii) evaluating the combined effects of climate variability and land use/land cover change on the hydrological components at the basin and sub-basin scales. Three historical classified land use maps of the Kilombero sub-basin were used to epitomize land-use change on this watershed (1990, 2002, and 2019), and three historical climate datasets (1990-2000, 2001-2010, and 2011-2019) were used to establish SWAT models for the watershed. To simulate the water balance, SWAT was calibrated, validated, and used in three different scenarios. From 1990 to 2019, the increased precipitation resulted in increased surface runoff, i.e. water yield. The temperature rise caused ET to increase in the summer, spring, and autumn. The diminished runoff, water yield, and ET was seen in winter. LULC change, on the other hand, could have a minor effect on the water balance compared to climate variability. On a yearly basis, ix surface runoff may increase steadily, but ET and water yield may fall. On a year-by-year and season-by-season basis, in both basin and sub-basin scales, LULC change and climate variability combined consequences on water balance were almost identical to the variance pattern of climate variability alone. ET increased for a time due to rising temperatures, which increased solar radiation and humidity, but ET decreased due to the fall of vegetation as the forest was deforested. Surface runoff decreased in some years due to increasing temperatures and declining precipitation. However, it increased in others due to high precipitation and the region's loss of forest, which removed vegetation cover and reduced surface roughness. Total water yield fell between 2000 and 2010 as precipitation dropped but rose between 2011 and 2019 as precipitation in the Kilombero sub-basin increased. The findings of this study add to our understanding of potential stream flow supply and can help with planning for water resource management in the study area.