Modeling the Potential for Water Supply from a Constructed Lake in South Mississippi Under Present Climate and Projected Climate Change

Author(s): Pote, J.; Wax, C.; Tagert, M.

The daily volume of water in a 5200 acre lake with a full capacity of 104,000 A-F in a coastal Mississippi location is simulated from 1961-2010. The lake basin is 17,550 acres, a runoff coefficient of 0.7 is used, base flow is set at 3 A-F/d, infiltration rate is set at 12 A-F/d, and outflow is set at 3 A-F/d. Inputs from the present climate regime are precipitation (P) minus potential evaporation (PE). Positive daily P-PE adds water to the lake and daily negative P-PE subtracts water from the lake. Climate change is projected by reducing daily P by 1.57% and increasing daily PE by 9.73%.

Cumulative P-PE for the average of all 50 years, the wettest year (1961), the median year (1993), and the driest year (2000), with and without climate change, is calculated. Factoring in the daily interaction between P and PE and comparing the present and changed climate by graphing the cumulative effect through the year shows that the annual pattern stays relatively the same day-by-day through each of the years and that the modeled climate change does reduce the end result in each of the years. For example, the average curves in both graphs show that under present climate the year ends at 19.77" but with climate change it ends at 13.85", a reduction of 5.32" or about 28% of the extra water. The median year curves show that without climate change the year ends at 24.55" but with climate change it ends at 19.75", a reduction of 4.8" or about 20% of excess water. The wettest year curves show the year ending at 54.65" but with climate change it ends at 48.40", a reduction of 6.55" or about 12% of extra water. The driest year curves show the year ending at -10.93" but with climate change it ends at -15.97, an increase in the year's deficit of 5.04" or about 46%.

Even in light of these potential changes in the average and extreme years, a 50-year daily analysis shows that both without and with climate change, the lake's volume drops no lower than about 97,000 A-F at any point in the period. The conclusion is that the climate of coastal Mississippi will sustain a surface water supply from a lake through known climate variability and proposed climate change in the future.

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