Environmental controls on stable isotope precipitation values over Mali and Niger,West Africa |
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| Authors: | Alexandra Lutz James M Thomas Anna Panorska |
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| Institution: | (1) Desert Research Institute, University and Community College System of Nevada, 2215 Raggio Parkway, Reno, NV 89512, USA;(2) Department of Math and Statistics, University of Nevada, Reno, NV 89512, USA |
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| Abstract: | This study evaluated the effects of the environmental factors precipitation amount (P), temperature (T), and vapor pressure (V
p) on the stable isotope composition (δ) of precipitation and the excess-deuterium (d) parameter in Mali and Niger, West Africa. At both locations, δ values were greatly affected by seasonal climatic conditions and a statistically significant negative correlation was observed
between δ and P. In Mali, a statistically significant negative correlation was also observed between δ and V
p. There was no statistically significant correlation between δ and T. Mean-weighting of δ values may be masking both dry-season and individual storm event precipitation phenomena, which are otherwise observed in
arithmetically averaged δ values. Mean monthly d values for peak monsoonal months indicate that precipitation is first-fraction, gaining little recycled water on its journey
inland from the Atlantic Ocean near the equator. Agreement between rainy-season precipitation and groundwater δ values, specifically peak monsoonal months, indicates that groundwater is being recharged by infiltration of current monsoonal
rains and is not paleo-groundwater recharged under past climatic conditions. Similarity between rainy-season precipitation
and groundwater d values provide another indication that monsoonal precipitation under current climatic conditions is the source of groundwater
recharge. The knowledge that groundwater is recently recharged monsoonal rains, rather than paleo-groundwater, is important
for evaluating groundwater sustainability and the effects that climate change will have on water resources. Understanding
and predicting changes in precipitation amounts and intensities, which ultimately affect timing and amount of groundwater
recharge, is critical for water resource management. |
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