Seasonal to interannual variations of soil moisture measured in Oklahoma

Abstract

Agriculture is a $2 billion component of the state economy in Oklahoma. As a result, meteorological, climatological, and agricultural communities should benefit from an improved understanding of soil moisture conditions and how those conditions vary spatially and temporally. The Oklahoma Mesonet is an automated observing network that provides realtime hydrometeorological observations at 115 stations across Oklahoma. In 1996, sensors were installed at 60 Mesonet sites to provide near-real-time observations of soil moisture.This study focuses on 6 years of soil moisture data collected between 1997 and 2002 to analyse the annual cycle and temporal characteristics of soil moisture across Oklahoma. The statewide analysis of the annual cycle of soil moisture revealed four distinct soil moisture phases. In addition, the four statewide phases were also observed in each of the nine climate divisions across Oklahoma, although the temporal characteristics of each phase were unique for each division. Further analysis demonstrated that, at shallow soil depths (5 and 25 cm), the spatial variability of soil moisture across Oklahoma was most homogeneous during the winter and spring periods and most heterogeneous during the summer and autumn periods. Conversely, at greater depths (60 and 75 cm), soil moisture was most heterogeneous during the winter period and the most homogeneous during the late spring.

Estimating root zone soil moisture using near-surface observations from SMOS

“…Soil moisture recharge occurs during the winter months. These patterns are similar to those reported by Illston et al (2004). There is relatively little intra-annual variation in mean monthly CV, although soil moisture at 5 cm is consistently more variable than at 25 and 60 cm.…”

“…Figure 8a also shows a marked drop in NS between February and April, with an NS < 0.3 in March. Illston et al (2004) observed four distinct seasonal soil moisture regimes in Oklahoma. The transition between the first regime and second regime (February-April) is characterized by the initiation of 5 cm soil moisture drying beginning in mid-March, while 25 cm soil moisture drying does not initiate until early-to-mid April.…”

“…Soil moisture in the North American Great Plains exhibits high variability both annually and interannually (Illston et al, 2004). Soil moisture not only varies over space and time, but also with depth in the soil column (Mahmood and Hubbard, 2004).…”

Detecting Wind Farm Impacts on Local Vegetation Growth in Texas and Illinois Using MODIS Vegetation Greenness Measurements

“…Doing so will help to quantify whether the plant seasonal cycle is modified by WFs. For example, during the peak growing season in JJA when SM is mostly limited due to higher temperatures and lower rainfall [44], the WT-enhanced vertical mixing may accelerate the SM deficit and thus inhibit vegetation growth due to enhanced ET, while during the vegetation greenup period when SM is adequate, the WT-enhanced vertical mixing may benefit plant growth. Such analysis will reveal whether there are noticeable changes in the plant seasonal cycle and whether the timing of such changes is due to the operating WTs.…”

Spatial and temporal variability of urban soil water dynamics observed by a soil monitoring network

“…Characteristic soil hydrological features for vegetation periods in temperate latitudes are a high initial soil water content in spring due to residual water from winter precipitation (snow and ice melt), a comparably dry summer season, and a rewetting of soil in fall (Illston et al 2004). This shape of a typical course of water content in soil will be referred to as the Bsinusoidal annual cycle.^It is mainly caused by meteorological characteristics in mid-latitude areas and modified by soil physical properties and vegetation.…”