Correlating Annual Piche Evaporation over Sudan and South Sudan to Latitudes, Longitudes and Altitudes

Abstract

Piche evaporation in mm/day for Sudan and South Sudan  for the period 1961- 1990 was obtained as normal data for 42 stations, and analyzed for correlations between  evaporation on the one hand and latitudes, longitudes and elevations on the other hand. Excel statistical package was used for analysis. Data was analyzed for the whole of Sudan and South Sudan. For the 42 stations, evaporation increased on average with increase in latitudes at a rate of about 0.67 mm/degree showing a highly significant linear correlation (P= 4.95E-07). When the 5 Red Sea stations were removed, analysis for the 37 stations resulted in higher significance (P = 4.61E-14), and evaporation increased at a rate of about 0.98 mm/degree latitude. When 5 South Sudan stations were removed, the increase in evaporation per degree latitude for the 32 stations was 0.96 mm/degree, almost similar to that for the 37 stations. Analysis for longitudes using 42 stations showed week or no significant correlation with evaporation, but demonstrated three clear localized patterns two of which showed a strong correlation between evaporation and longitudes; a South Sudan almost flat trend, a western Sudan moderate slope trend where evaporation decreased at about 0.52 mm/ degree longitude east and a general steep slope trend where evaporation decreased at a rate of about 1.1 mm/ degree longitude. Using 32 stations for Sudan, longitudes showed once again the two different evaporation patterns; the western Sudan trend with almost the same slope and the general steep slope trend with also similar slope. Altitudes on the other hand showed no clear correlation to evaporation when all the 42 stations were considered. When the South Sudan and Red Sea stations were removed, the remaining 32 stations showed significant (P= 0.01) correlation with evaporation which declined at a rate of about 0.01 mm/meter above sea level.

Key Words: Piche evaporation, Latitude, Longitude, Altitude, Sudan