Quantifying agricultural drought in tallgrass prairie region in the U.S. Southern Great Plains through analysis of a water-related vegetation index from MODIS images

Authors: ZHOU, YUTING - University Of Oklahoma; XIAO, X. - University Of Oklahoma; ZHANG, G. - University Of Oklahoma; Wagle, Pradeep; BAJGAIN, R. - University Of Oklahoma; DONG, J. - University Of Oklahoma; JIN, C. - University Of Oklahoma; BASARA, J. - University Of Oklahoma; Anderson, Martha; HAIN, C. - Goddard Space Flight Center; OTKIN - University Of Wisconsin

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2017
Publication Date: 8/21/2017
Citation: Zhou, Y., Xiao, X., Zhang, G., Wagle, P., Bajgain, R., Dong, J., Jin, C., Basara, J., Anderson, M.C., Hain, C., Otkin 2017. Quantifying agricultural drought in tallgrass prairie region in the U.S. Southern Great Plains through analysis of a water-related vegetation index from MODIS images. Agricultural and Forest Meteorology. 246:111-122.

Interpretive Summary: Many drought indicators have been developed to track agricultural drought. This is necessary; research has demonstrated that, given the complexity of the drought phenomenon, no single indicator can adequately capture all impacts on all agricultural sectors. Different indicators perform better for different crops under different climatic conditions. This paper explores the performance of the Land Surface Water Index (LSWI) in capturing drought signals in the tallgrass prairie region of the Southern Great Plains, which has been affected by severe droughts in recent years impacting rangeland productivity. The LSWI is computed as a band ratio from satellite imagery collected in the near infrared and shortwave infrared wavebands, and has demonstrated good response t in this ecosystem o rainfall variability in prior research. Here, LSWI response was evaluated over three growing seasons, from 2010 to 2012, and compared to responses in other standard drought indicators that are focused on agricultural drought impacts, including the United States Drought Monitor (USDM). The results showed comparable response between these indicators, but with unique information conveyed by the LSWI. The LSWI showed good agreement with precipitation gradients across the study domain, and was able to quantify frequency of summer drought occurrence that was consistent with observations. Future work will focus on identifying LSWI thresholds that clearly delineate regions impacted by agricultural drought and the severity of the associated impacts.

Technical Abstract: Severe droughts in the Southern Great Plains (SGP: Kansas, Oklahoma, and Texas) in recent years have reduced the productivity of tallgrass prairie and resulted in substantial economic losses to the beef cattle industry in this region. Understanding spatial and temporal patterns of agricultural drought in the SGP can help ranchers to develop and implement drought mitigation strategies. In this study, the Land Surface Water Index (LSWI), calculated from the Moderate Resolution Imaging Spectroradiometer (MODIS) near infrared and shortwave infrared bands, was used to assess agricultural drought in the tallgrass prairie region of the SGP during 2000-2013. The number of consecutive days with LSWI < 0 (DNLSWI) during the growing season was defined as the drought duration, which was then used to identify and analyze frequency of summer drought and whole growing season drought (WGSD). The spatial pattern of DNLSWI was consistent with the east-to-west decreasing precipitation gradient across the SGP region. Summer drought duration as depicted by the DNLSWI in the western portion of the study area was around one and a half month. The occurrence of WGSD increased from one year in the east to up to six years in the west, demonstrating the susceptibility of the tallgrass prairie region to drought. In addition to the total amount of precipitation, its intra-annual distribution also played an important role in drought development. A comparison with other widely used national drought products, namely the Evaporative Stress Index (ESI), the Vegetation Drought Response Index (VegDRI), and the United States Drought Monitor (USDM), shows good agreement with the LSWI-based drought depictions. Quantitative analyses indicate that LSWI-based drought agreed better with ESI in severe drought conditions than in moderate or pre-drought conditions. Severe drought periods characterized by the USDM also had low LSWI values. The areas affected by drought derived from the LSWI-based drought index were significantly correlated with hay production. As an indicator of vegetation water stress at moderate spatial resolution (~500 m), the LSWI has the potential to show drought conditions for an individual ranch and offer guidance for drought mitigation activities and livestock production.