Links Between Southeastern Arizona Soil Moisture and El Niño-Southern Oscillation

Previous studies have shown that least 40% of the annual precipitation occurs during the months of July, August and September in the southwestern United States. These months correspond with the climatological North American Monsoon (NAM) period. The NAM precipitation is a major driver of hydrologic conditions in the southwest United States. Studies also show that soil moisture conditions are primarily driven by precipitation. Modelling studies have hypothesized links between El Niño-Southern Oscillation (ENSO), winter/summer soil-moisture conditions, monsoon onset, and monsoon strength. However, these studies often lacked in-situ soil moisture observations, and instead inferred soil moisture conditions from the Palmer Drought Severity Index or estimated soil moisture conditions using hydrological model simulations. This study represents a first attempt at relating in-situ soil-moisture measurements with ENSO and NAM precipitation variability. NOAA’s Earth System Research Laboratory Physical Sciences Division Soil Moisture Network (SMN) maintains a set of stations that measure air temperature, precipitation, soil temperature, and volumetric water content in the Babocomari river basin. The basin is located in Southeastern Arizona and is a tributary of the San Pedro River. Water from the San Pedro and Babocomari rivers help recharge the aquifers that supply water for both agriculture and domestic water use in the region. The river also supports the San Pedro Riparian National Conservation Area. The results shown in this study indicate that precipitation from July to September occurring in the Babocomari river basin accounted for 60 % – 70 % of the observed annual precipitation. Statistical analyses shown in this study suggest that there are no clear links between the Multivariate ENSO Index (MEI), station precipitation, observed soil water content, and monsoon onset/delay.