REVIEW ARTICLE Vegetation productivity responses to drought on tribal lands in the four corners region of the Southwest USA Mohamed Abd Salam EL-VILALY (✉) 1 , Kamel DIDAN 2 , Stuart E. MARSH 3 , Willem J.D. VAN LEEUWEN 3 , Michael A. CRIMMINS 4 , Armando Barreto MUNOZ 2 1 The International Food Policy Research Institute, Washington, DC 20006-1002, USA 2 Vegetation Index and Phenology Lab, Department of Agricultural and Biosystems Engineering, The University of Arizona, Tucson, AZ 85721-0036, USA 3 Arizona Remote Sensing Center, School of Natural Resources and the Environment, The University of Arizona, Tucson, AZ 85721-0043, USA 4 Department of Soils Water and Environmental Science, The University of Arizona, Tucson, AZ 85721-0038, USA © Higher Education Press and Springer-Verlag Berlin Heidelberg 2017 Abstract For more than a decade, the Four Corners Region has faced extensive and persistent drought conditions that have impacted vegetation communities and local water resources while exacerbating soil erosion. These persistent droughts threaten ecosystem services, agriculture, and livestock activities, and expose the hypersensitivity of this region to inter-annual climate variability and change. Much of the intermountain Western United States has sparse climate and vegetation monitoring stations, making fine-scale drought assessments difficult. Remote sensing data offers the opportunity to assess the impacts of the recent droughts on vegetation productivity across these areas. Here, we propose a drought assessment approach that integrates climate and topographical data with remote sensing vegetation index time series. Multi- sensor Normalized Difference Vegetation Index (NDVI) time series data from 1989 to 2010 at 5.6 km were analyzed to characterize the vegetation productivity changes and responses to the ongoing drought. A multi-linear regres- sion was applied to metrics of vegetation productivity derived from the NDVI time series to detect vegetation productivity, an ecosystem service proxy, and changes. The results show that around 60.13% of the study area is observing a general decline of greenness (p < 0.05), while 3.87% show an unexpected green up, with the remaining areas showing no consistent change. Vegetation in the area show a significant positive correlation with elevation and precipitation gradients. These results, while, confirming the region’s vegetation decline due to drought, shed further light on the future directions and challenges to the region’s already stressed ecosystems. Whereas the results provide additional insights into this isolated and vulnerable region, the drought assessment approach used in this study may be adapted for application in other regions where surface- based climate and vegetation monitoring record is spatially and temporally limited. Keywords drought, remote sensing, Hopi, Navajo Nation 1 Introduction Globally more than 807 droughts were recorded between 1900 and 2004, impacting more than 1.8 billion people, with 11 million deaths, and billions of dollars in economic losses (Below et al, 2007; UNESCO, 2012). Due to their multiple impacts on global agricultural, hydrological, eco- environmental, and social-economical systems, droughts have been categorized the second most geographically widespread hazard after floods according to the United Nations Educational Scientific and Cultural Organization (UNESCO, 2012). Droughts are classified among all the natural hazards as the most devastating hazard when the number of people affected by drought is taken into considerations (Obasi, 1994; Keshavarz et al., 2013). From the 1970s to the early 2000s, the percentage of Earth’s land area experiencing very severe droughts doubled, according to the U.S. National Center for Atmospheric Research (NCAR, 2005). Degradation of natural resources has become one of the major dominating issues threating ecosystem structures, functions, and services in arid and semi-arid environments. Over 40% of the world’s land surface, with more than one billion people, is considered arid and semi-arid (UNDP/ Received June 28, 2016; accepted February 5, 2017 E-mail: a.s.elvilaly@cgiar.org Front. Earth Sci. DOI 10.1007/s11707-017-0646-z