Impact of climate change on groundwater dynamics in Nzega district.

Groundwater resource is the major source of drinking water in Sub-Saharan Africa but there is lack of reliable and timely information on the status of groundwater supplies. The aim of this study was to define long term climate change trends and its impacts on groundwater dynamics in Nzega District, Tanzania. Both quantitative (borehole and household surveys) and qualitative (participatory village meeting and key informant interview) methods were used. Detailed analysis of long-temp climate data (1925-2008) in various scenarios was done using spreadsheet. Recharge rates were estimated by empirical method of rainfall-recharge relationship. Surveys were analysed by SPSS program and qualitative data manually through structural and content analysis. Survey results show that climate has changed by both increased temperature (79%, N= 100) and decreased rainfall (61%, N=100) causing groundwater excavation depth to increase from several 1.5 meters (in 1975) to beyond 20 meters deep (in 2010). Frequency and duration of drying of surface water sources and shallow wells during dry season had increased leaving majority of population entirely dependent on boreholes. Climate data showed that both minimum and maximum average monthly temperatures increased from past (1960-1989) to present (1990- 2008). Both annual average- maximum and minimum temperature also increased by 1 .3oc and 1 .2oC, respectively, with 0.3o C per decadal increase of total annual average temperature. Rainfall used to cease from mid-April but currently starts to cease in early March. Moreover, in the past the district experienced two peaks of maximum rainfall (December and Mid-April), but currently only one maximum peak is observed in December. Total annual rainfall decreased by 11.8 mm (1.5%) from past 1925-1955) to present (1986-2008) resulting into decreased annual groundwater recluse rate by 2.3%. Climate has changed by both increasing temperature and decreased rainfall including change of rainfall pattern, cessation time and duration, thus, impacting ground water dynamics negatively. There is, therefore, substantial need to continuously monitor groundwater systems and recharge in an integrated manner.