Soil Moisture Variability in Iowa

Thirty years (1954-1983) of soil moisture data from 60 sites in Iowa are used to identify the dominant modes of spatial and temporal variability. There is no evidence of long-term trends in soil moisture during this period; however there is an influence from El Niño- Southern Oscillation (ENSO). There is also a pronounced annual soil moisture cycle that has three distinct phases; a moist phase, a drying phase, and a recharge phase. Both soil moisture and precipitation exhibit a northwest to southeast gradient, with wetter conditions in the northwest and drier conditions in the southeast. Spatial variations in climate and soil characteristics are responsible for these spatial patterns. Finally, the abnormality of the 2012 drought is put into context as drought frequency and magnitude were calculated and compared.