During the summer of 2007, the state of Oklahoma had its fourth wettest summer (June-August) on record. This period was marked by heavy, persistent rains and flooding that devastated parts of the state. In June alone, some areas of Oklahoma received over 400mm of precipitation, shattering climatological records for that month. Typically Oklahoma receives little precipitation and soil moisture decreases during the summer. However, due to the large quantity of precipitation during the summer of 2007, soil moisture conditions were extremely moist which further impacted the partitioning of the surface fluxes between latent and sensible heat.

In the late spring of 2007, ten eddy covariance flux towers were deployed portions of central Oklahoma in four study sites within the Cloud and Land Surface Interaction Campaign (CLASIC). These eddy covariance flux towers were placed in areas with varying surface conditions, ranging from forest to pasture to agricultural fields. Prior to, during, and following the CLASIC period, observations of the surface energy balance data was continuously collected including variables such as the sensible, latent, and ground heat fluxes.

Using the data collected during CLASIC as well as Oklahoma Mesonet observations, the spatial and temporal variability of the surface energy budget and soil moisture during the period of June to August 2007 were analyzed. In particular, the focus of the study was placed on the variability of (a) the evaporative fraction and (b) the fractional water index of soil moisture. Time series plots revealed little variability in evaporative fraction throughout the period for sites located over pasture. However, significant variability in evaporative fraction was found for sites located on agricultural fields due to rapid changes in vegetation conditions.