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James Verdin

Publications and source records attributed to James Verdin.

28 records · Page 2Linked to original sources
USGS2012

Future opportunities and challenges in remote sensing of drought

The value of satellite remote sensing for drought monitoring was first realized more than two decades ago with the application of Normalized Difference Index (NDVI) data from the Advanced Very High Resolution Radiometer (AVHRR) for assessing the effect of drought on vegetation. Other indices such as the Vegetation Health Index (VHI) were also developed during this time period, and applied to AVHRR NDVI and brightness temperature data for routine global monitoring of drought conditions. These early efforts demonstrated the unique perspective that global imagers such as AVHRR could provide for operational drought monitoring through their near-daily, global observations of Earth's land surface. However, the advancement of satellite remote sensing of drought was limited by the relatively few spectral bands of operational global sensors such as AVHRR, along with a relatively short period of observational record. Remote sensing advancements are of paramount importance given the increasing demand for tools that can provide accurate, timely, and integrated information on drought conditions to facilitate proactive decision making (NIDIS, 2007). Satellite-based approaches are key to addressing significant gaps in the spatial and temporal coverage of current surface station instrument networks providing key moisture observations (e.g., rainfall, snow, soil moisture, ground water, and ET) over the United States and globally (NIDIS, 2007). Improved monitoring capabilities will be particularly important given increases in spatial extent, intensity, and duration of drought events observed in some regions of the world, as reported in the International Panel on Climate Change (IPCC) report (IPCC, 2007). The risk of drought is anticipated to further increase in some regions in response to climatic changes in the hydrologic cycle related to evaporation, precipitation, air temperature, and snow cover (Burke et al., 2006; IPCC, 2007; USGCRP, 2009). Numerous national, regional, and global efforts such as the Famine and Early Warning System (FEWS), National Integrated Drought Information System (NIDIS), and Group on Earth Observations (GEO), as well as the establishment of regional drought centers (e.g., European Drought Observatory) and geospatial visualization and monitoring systems (e.g, NASA SERVIR) have been undertaken to improve drought monitoring and early warning systems throughout the world. The suite of innovative remote sensing tools that have recently emerged will be looked upon to fill important data and knowledge gaps (NIDIS, 2007; NRC, 2007) to address a wide range of drought-related issues including food security, water scarcity, and human health.

Book chapter↗
USGS2012

A climate trend analysis of Senegal

This brief report, drawing from a multi-year effort by the U.S. Agency for International Development (USAID) Famine Early Warning Systems Network (FEWS NET), identifies modest declines in rainfall, accompanied by increases in air temperatures. These analyses are based on quality-controlled station observations. Conclusions: * Summer rains have remained steady in Senegal over the past 20 years but are 15 percent below the 1920-1969 average. * Temperatures have increased by 0.9° Celsius since 1975, amplifying the effect of droughts. * Cereal yields are low but have been improving. * The amount of farmland per person is low and declining rapidly. * Current population and agriculture trends could lead to a 30-percent reduction in per capita cereal production by 2025.

Fact Sheet↗
USGS2012

Food security in a changing climate

By 2080 the effects of climate change—on heat waves, floods, sea level rise, and drought—could push an additional 600 million people into malnutrition and increase the number of people facing water scarcity by 1.8 billion. The precise impacts will, however, strongly depend on socioeconomic conditions such as local markets and food import dependence. In the near term, two factors are also changing the nature of food security: (1) rapid urbanization, with the proportion of the global population living in urban areas expanding from 13 percent in 1975 to greater than 50 percent at present, and (2) trade and domestic market liberalization since 1993, which has promoted removal of import controls, deregulation of prices, and the loss of preferential markets for many small economies. Over the last two years, the worst drought in decades has devastated eastern Africa. The resulting food-security crisis has affected roughly 13 million people and has reminded us that there is still a long way to go in addressing current climate-related risks. In the face of such profound changes and uncertainties, our approaches to food security must evolve. In this article, we describe four key elements that, in our view, will be essential to the success of efforts to address the linked challenges of food security and climate change.

Solutions Journal↗
USGS2007

Development of a global slope dataset for estimation of landslide occurrence resulting from earthquakes

Landslides resulting from earthquakes can cause widespread loss of life and damage to critical infrastructure. The U.S. Geological Survey (USGS) has developed an alarm system, PAGER (Prompt Assessment of Global Earthquakes for Response), that aims to provide timely information to emergency relief organizations on the impact of earthquakes. Landslides are responsible for many of the damaging effects following large earthquakes in mountainous regions, and thus data defining the topographic relief and slope are critical to the PAGER system. A new global topographic dataset was developed to aid in rapidly estimating landslide potential following large earthquakes. We used the remotely-sensed elevation data collected as part of the Shuttle Radar Topography Mission (SRTM) to generate a slope dataset with nearly global coverage. Slopes from the SRTM data, computed at 3-arc-second resolution, were summarized at 30-arc-second resolution, along with statistics developed to describe the distribution of slope within each 30-arc-second pixel. Because there are many small areas lacking SRTM data and the northern limit of the SRTM mission was lat 60?N., statistical methods referencing other elevation data were used to fill the voids within the dataset and to extrapolate the data north of 60?. The dataset will be used in the PAGER system to rapidly assess the susceptibility of areas to landsliding following large earthquakes.

Open-File Report↗
USGS2005

Recent drought tendencies in Ethiopia and equatorial-subtropical eastern Africa

This report presents an analysis of Ethiopian rainfall from 1960 through 2004, based on 186 gauges in Ethiopia and 373 gauges from surrounding countriesi. Substantial post1997 declines in March-September rainfall have been observed in the northeast, southeast and southwestern portions of the country, a result corroborated by several independent data sourcesii. The observed rainfall reductions have been accompanied by an increase in millions needing food aid (Figure 1). The greatest percent decrease has occurred during the Belg (March-May) season, though Kiremt (June-September) rains have also diminished in many areas. This recent dryness may be linked to a warming tendency in the southern Indian Oceaniii, and is likely to impact densely populated and/or water-insecure regions of southern and eastern Ethiopia. These areas face declines in rainfall and increasing demands on land, water and agriculture. Recent dryness, dropping coffee prices, rising population and land degradation combine to create mounting destitution that must be countered with innovative planning and policiesiv. This report is organized as follows. Section 1 provides context for our results by summarizing recent trends in food aid, precipitation and the regional climate. Section 2 quantifies the water availability situation by analyzing potentially available runoff. Section 3 describes the results of our historical rainfall analysis. Section 4 relates the observed rainfall variations to circulation and sea surface temperature patterns in the Indian and Pacific Oceans. Section 5 briefly summarizes our results.

Equatorial-subtropical Africa↗
USGS2003

Estimating Meher crop production using rainfall in the 'Long Cycle' region of Ethiopia

Meher season crop production is well correlated with April-May rainfall in the Ethiopian 'long cycle' crop growing region. This relationship is used to estimate 2003 Meher small farmer gross production at 87 =B1 10 million quintals (8.7 million MT 2 =B1 1 million MT) of cereals, pulses and other crops, using data from the Central Statistical Authority (CSA). Assuming recent levels of commercial and food aid imports, Belg production and population growth, this estimate will produce a food deficit of about 23 million quintals (2.3 million MT) for 2003-04, smaller than the one experienced during 2002-03 (34 million Qt, or 3.4 million MT), but similar to the deficit experienced in 1997-98. A long-term negative rainfall trend in the southwestern highlands may be aggravating the situation. Increasing food requirements and decreasing precipitation point toward chronic food shortages in the near future.

FEWS NET Special Report↗
USGS2002

Evaluating the performance of a crop water balance model in estimating regional crop production

The comparison between a spatially distributed crop index and reported yield was evaluated. The crop index was generated by a crop water balance model that simulates the reduction of crop yield (as a percentage of the potential) due to water deficit. This model is currently operational as a monitoring and forecasting tool for region-wide food security analyses in drought prone countries in Sub-Saharan Africa. The most important input parameters of the model are Africa-wide satellite-based rainfall estimate images and spatially distributed potential evapotranspiration images calculated from 6-hourly numerical weather model data. District level crop yield data from Ethiopia were used to evaluate the performance of the model. Historical sorghum yield data from 1996-1999 were used to evaluate the performance of a seasonal water requirement satisfaction index (WRSI) for sorghum. WRSI values and reported district yield data were significantly correlated. The WRSI model was particularly successful in capturing the response of the crop during a relatively dry year. In districts that never experienced water deficit during the study period, it was possible to infer the magnitude of yield variability that was caused by factors other than water supply.

Sub-Saharan Africa↗
USGS2002

A flood early warning system for southern Africa

Sizeable areas of the Southern African Region experienced widespread flooding in 2000. Deployment of hydrologic models can help reduce the human and economic losses in the regions by providing improved monitoring and forecast information to guide relief activities. In this study, we describe a hydrologic model developed for wide-area flood risk monitoring for the Southern African region. The model is forced by daily estimates of rainfall and evapotranspiration derived from remotely sensed data and assimilation fields. Model predictive skills were verified with data observed stream flow data from locations within the Limpopo basin. The model performed well in simulating the timing and magnitude of the stream flow during a recent episode of flooding in Mozambique in 2000.

Conference Paper↗
USGS2000

Data and applications for study of the water cycle in Africa

There are a number data set development, data dissemination, and applications activities at the U.S. Geological Survey (USGS) that contribute to the study of the water cycle in Africa. Some of these stem from global change research initiatives, while others are the result of technical assistance provided to international development and humanitarian assistance projects. Data themes include topography and related hydrological derivatives, land cover, satellite rainfall estimates, and vegetation indices. Some data sets are USGS products, while others originate from cooperating agencies like NASA and NOAA and are distributed secondarily. In Africa, applications include agrometeorological estimates, drought and flood monitoring. Many of the data sets are available to the user community without charge by internet, or at cost of reproduction on CDROM and tape media.

Conference Paper↗