Data on monthly precipitation, temperature, Palmer drought severity index(PDSI) and Palmer "Z" index (ZNDX) for 72 climate divisions in the United States (US) Midwest covering the period 1895-1995 were analyzed statistically for evidence of land surface-atmosphere feedbacks during the warm season (April-September). Previous work in this area suggests that springtime precipitation may help determine the temperature regime of the following summer, presumably via the moisture content of the upper soil. The emphasis is on documenting climatic impacts of land surface anomalies, such as drought and extended wet periods; and land cover transformations due to human activities. These are central concerns of large-scale monitoring programs (e.g., GEWEX and GOALS) within the global change community.
Results indicate fairly strong inter-seasonal and inter-annual persistence in both moisture (precipitation, ZNDX and PDSI) and temperature conditions. Specifically, warm springs tend to be followed by warm and dry summers, which also follow warm and dry summers of the preceding year. These results suggest that the soil moisture in the Midwest exerts some influence on the overlying thermal profile through alterations of latent and sensible heat.
Additional analysis of the synoptic conditions for years having both similar and dissimilar soil moisture conditions in the spring and summer showed no strong association with synoptic types.
This suggests that the land surface-climate association is reasonably maintained across different circulation patterns. The aforementioned results do not fully address the possibility that simple
persistence of climatic conditions between seasons may be at least partly responsible for the significant associations between temperature and moisture. Moreover, the relationship does not seem to hold for years marked by extremes in ENSO.