Spatial and elevational variations of summer rainfall in the U.S. Southwest.

MICHAUD J.D., AUVINE B.A., PENALBA O.C

JOURNAL OF APPLIED METEOROLOGY

AMS

Año: 1995 vol. 34 p. 2689 - 2703

0894-8763

This study examines the spatial variability of mean monthly summer rainfall in the southwestem United States, with special attention given to the effect of elevation. Rain gauge data from a consistent 60-yr period show that mean rainfall increases linearly with elevation within a local area. A simple model (rain = norrnalized rainfall as a function of latitude and longitude + elevation coefficient X elevation) explains a large part of the spatial variability of mean rainfall. The rainfall model (the MSWR model) and digital elevation data were used to produce a 10 X 10 gridded rainfall climatology for July, August, and September. Regional rainfall estimated with this model is 9.3% higher than an estimate based on arithmetic averaging ofgauge data over 20 X 20 areas. For individual 20 X 20 cells, the difference between model rainfall and the arithmetic mean of gauge rainfall ranged frorn -250% to +41%. The MSWR model was used to remove oragraphic effects from regional rainfall fields. When rainfall is norrnalized to sea level, two rainfall maximums emerge: one in south-central Arizona associated with the Mexican monsoon maximum and one in southeastem New Mexico associated with the Gulf ofMexico. Detrended block kriging (using the MSWR model as an estimate of the long-term trend) and monthly rain gauge data were used to produce unbiased areal rainfall estimates that were compared to 10 X 10 satellite-based rainfall estimates. On a month-by-month basis, there were large differences between the two estimates, although the comparison improved after temporal averaging.