Robert Hijmans

Robert Hijmans
University of California, Davis | UCD · Department of Environmental Science and Policy

PhD

About

206
Publications
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Introduction
Skills and Expertise

Publications

Publications (206)
Article
Full-text available
Crop yield estimation from satellite data requires field observations to fit and evaluate predictive models. However, it is not clear how much field data collection methods matter for predictive performance. To evaluate this, we used maize yield estimates obtained with seven field methods (two farmer estimates, two point transects, and three crop c...
Article
Full-text available
Agricultural index insurance contracts increasingly use remote sensing data to estimate losses and determine indemnity payouts. Index insurance contracts inevitably make errors, failing to detect losses that occur and issuing payments when no losses occur. The quality of these contracts and the indices on which they are based, need to be evaluated...
Article
Full-text available
Crop yields across sub-Saharan Africa are much lower than what is attainable given the environmental conditions and available technologies. Closing this ‘ecological yield gap’ is considered an important food security and rural welfare goal. It is not clear, however, whether it is economically sensible for farmers to substantially increase crop yiel...
Article
The increasing availability of satellite data at higher spatial, temporal and spectral resolutions is enabling new applications in agriculture and economic development, including agricultural insurance. Yet, effectively using satellite data in this context requires blending technical knowledge about their capabilities and limitations with an unders...
Article
Full-text available
Local food prices are key indicators of food security and market conditions. Yet price data are often not available, particularly for rural areas of Sub-Saharan Africa. We compiled data from 168 markets to study spatial and temporal price variation. We found that prices slightly increase when the preceding growing season was dry. Across the contine...
Article
Full-text available
Species distribution models (SDMs) are widely used to predict and study distributions of species. Many different modeling methods and associated algorithms are used and continue to emerge. It is important to understand how different approaches perform, particularly when applied to species occurrence records that were not gathered in struc­tured sur...
Article
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Obtaining detailed data on the spatio-temporal variation in crop phenology is critical to increasing our understanding of agro-ecosystem function, such as their response to weather variation and climate change. It is challenging to collect such data over large areas through field observations. The use of satellite remote sensing data has made pheno...
Article
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Improving female empowerment is an important human rights and development goal that needs better monitoring. A number of indices have been developed to track female empowerment at the national level, but these are incomplete and may obscure important sub-national variation. We developed the Female Empowerment Index (FEMI) to track multiple domains...
Article
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Growing conditions for crops such as coffee and wine grapes are shifting to track climate change. Research on these crop responses has focused principally on impacts to food production impacts, but evidence is emerging that they may have serious environmental consequences as well. Recent research has documented potential environmental impacts of sh...
Article
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Low crop yields in Sub-Saharan Africa are associated with low fertilizer use. To better understand patterns of, and opportunities for, fertilizer use, location specific fertilizer price data may be relevant. We compiled local market price data for urea fertilizer, a source of inorganic nitrogen, in 1729 locations in eighteen countries in two region...
Article
The content of (1→3, 1→4)-β-glucan (BG) in barley (Hordeum vulgare L.) has become a breeding target due to the human health benefits of BG. More than 20,000 barley accessions from the USDA National Small Grains Collection (NSGC) have been assayed for BG content and the data recorded in the Germplasm Resources Information Network (GRIN). This study...
Article
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Increasingly large presence‐only survey datasets are becoming available for use in conservation assessments. Potentially, these records could be used to determine spatial patterns of plant species rarity and endemism. We test the integration of a large South Korean species record database with Rabinowitz rarity classes. Rabinowitz proposed seven cl...
Article
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Opportunities for and constraints to crop production can be assessed with crop growth simulation models. Most crop simulation models require daily weather data as input but such data are generally not available at a high spatial resolution. Several approaches have been developed to estimate yield potential (Yp) at locations without daily weather da...
Article
Air temperature (Ta) is commonly used for modeling rice phenology. However, since the growing point of rice is under water during the vegetative and the early part of the reproductive period, water temperature (Tw) is likely to have a greater influence on crop developmental rates than Ta during this period. To test this hypothesis, we monitored Tw,...
Article
Full-text available
The coexistence of different types of poultry operations such as free range and backyard flocks, large commercial indoor farms and live bird markets, as well as the presence of many areas where wild and domestic birds co-exist, make California susceptible to avian influenza outbreaks. The 2014–2015 highly pathogenic Avian Influenza (HPAI) outbreaks...
Data
Land cover classes and their pixel values in the raster used in the models. (DOCX)
Data
Spatial predictions from the original presence-absence MaxEnt (MPA), presence-absence Random Forest (RFPA), their respective sampling probabilities (M sampling, RF sampling) and the corrected Spatial predictions for MaxEnt (MPAc) and Random Forest (RFPAc). The color gradient of each pixel represents the presence probability from clear red shading (...
Data
Spearman Correlation plots for the four models (MPA, RFPA, MPB, RFPB). (TIF)
Data
Most important bird species sampled in the FluDB raw dataset. (DOCX)
Data
Important farmland map classes and their pixel values in the raster used in the models. (DOCX)
Data
Temporal sampling distribution of the FluDB raw dataset by month over the entire study period and by year. The blue color indicates the number of samples that tested negative and the red color represents the number of samples that tested positive. (TIF)
Data
Spatio-temporal sampling distribution per unique location of the FluDB raw dataset. The X axis indicates the year of sampling. The Y axis represents the coordinates of every single location sampled. The color gradient represents the percent of positive samples in that specific location per year. (TIF)
Data
Jackknife of regularized training gain of the variables included in the two MaxEnt models (MPA, MPB). The red bar represents the overall training gain with all the included variables. The blue bar represents the training gain when using each variable in isolation. The clear blue bar is the training gain when the variable is excluded from the model....
Data
Response curves for each of the four models (MPA, RFPA, MPB, RFPB). (TIF)
Article
Full-text available
The center of origin of maize is in Mexico and maize diversity is very high in many parts of the country. Here we describe and analyze the geographic distribution and diversity of maize using a database of 18,176 georeferenced observations of maize races. The number of observations by race follows the common “hollow curve” distribution, with six ra...
Article
Full-text available
Knowing where, when, and how much rice is planted and harvested is crucial information for understanding the effects of policy, trade, and global and technological change on food security. We developed RiceAtlas, a spatial database on the seasonal distribution of the world’s rice production. It consists of data on rice planting and harvesting dates...
Article
The mean height-for-age Z-score (HAZ) of children under five is an important indicator of the health status of a population. HAZ values are frequently aggregated and reported at the national level, potentially obscuring important within-country variation. We evaluated aggregation and interpolation methods to provide sub-national estimates over spac...
Article
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We created a new dataset of spatially interpolated monthly climate data for global land areas at a very high spatial resolution (approximately 1 km 2). We included monthly temperature (minimum, maximum and average), precipitation, solar radiation, vapour pressure and wind speed, aggregated across a target temporal range of 1970–2000, using data fro...
Article
Full-text available
Understanding dietary patterns is vital to reducing the number of people experiencing hunger (about 795 million), micronutrient deficiencies (2 billion), and overweight or obesity (2.1 billion). We characterize global trends in dietary quality by estimating micronutrient density of the food supply, prevalence of inadequate intake of 14 micronutrien...
Data
Average global micronutrient density from 1961–2011 by select food groups. Note: Bioavailability is not considered for most nutrients. Micronutrients in animal-source foods are generally more bioavailable, which is not considered here. (TIF)
Data
Per capita daily energy availability of rice and animal-source foods in Southeast Asia. (TIF)
Data
Compiled food composition table items. (CSV)
Data
Intake coefficients of variation. (CSV)
Data
Micronutrient densities and prevalence of inadequate intake. (CSV)
Data
Per capita daily energy availability of select food groups in sub-Saharan Africa. (TIF)
Data
Proportional availability of select food groups in sub-Saharan Africa. (TIF)
Data
Country-level estimated prevalence of inadequate intake of 9 micronutrients in 2011, excluding fortification. Values for countries with missing data (Libya and DRC) were estimated based on the values of neighboring countries. Source: S4 Dataset. (TIF)
Data
Impact of fortification. (CSV)
Article
Climate change is predicted to shift temperature regimes in most agricultural areas with temperature changes expected to impact yields of most crops, including rice. These temperature-driven effects can be classified into point stresses, where a temperature event during a sensitive stage drives a reduction in yield, or seasonal warming losses, wher...
Article
Full-text available
Describing spatiotemporal patterns of agricultural biodiversity may be an important step toward better understanding its effect on agroecosystem services. We describe species-level field crop diversity at the national and state level for the United States, using annual survey data for a 142-yr period. National-level field crop diversity was very lo...
Article
Full-text available
En la Estación Experimental Toralapa ubicada a 3,450 msnm, se estudió la influencia de la fertilización mineral sobre el desarrollo y la producción de oca e isaño con niveles de N P K de 80-160-80 kg/ha, frente a un testigo sin fertilización. En ambas especies, se observó un efecto marcado de la fertilización sobre el índice de área foliar, cobertu...
Article
Full-text available
Resumen En la gestión agrícola 1995-1996 se evaluó el desarrollo y crecimiento de los cultivos de papa, oca e isaño en la Estación Experimental Toralapa (3,450 msnm). Se realizaron observaciones en las fases de desarrollo considerando los macroestadíos (porcentaje de emergencia, inicio de la tuberización, inicio de la floración y madurez fisiológic...
Article
Full-text available
Understanding how predicted species responses to climate change are affected by advances in climate modeling is important for determining the frequency with which vulnerability assessments need to be updated. We used ecological niche models to compare predicted climatic habitat suitability for 132 species of reptiles and amphibians in California, U...
Code
This repository hosts R Scripts, now v1.1, and the data necessary for reproducing my work with metamodels used to map the global risk of potato late blight. This is done using blight units based on the SimCast model modified by Grünwald et al. (2002). Other scripts include tools to predict growing seasons using Ecocrop and estimating global late bl...
Article
Crop phenology models that use constant temperature parameters across developmental stages may be less accurate and have temperature-dependent systematic prediction error (bias). Using the DD10 model, we evaluated default and optimized (DD_Opt) temperature parameters using data from seven California rice (Oryza sativa L.) cultivars grown in six loc...
Article
An analytical framework is described for assessing the nutritional adequacy of national food supplies and the potential for addressing micronutrient gaps by increased crop production and crop diversity. The micronutrient contents of national food supplies of three countries (Bangladesh, Senegal, and Cameroon) were estimated using data from national...
Technical Report
Full-text available
Link: http://www.sciencecouncil.cgiar.org/system/files_force/ISPC_StrategyTrends_Metrics.pdf.
Article
Full-text available
The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpacea...
Article
AimEcological niche modelling is one of the main tools that allows for the incorporation of climate change effects into conservation planning. For example, ecological niche model predictions can be used to rank species by degree of predicted future habitat loss. While many studies have considered how different modelling decisions contribute to unce...
Conference Paper
Background/Question/Methods Ecological niche models are one of the main tools for conservation planning under future climate change. However, these models can produce complicated outputs that are difficult to incorporate into the planning process. A commonly employed approach is to collapse ecological niche model results into metrics that rank sp...
Conference Paper
Full-text available
Background/Question/Methods Protected areas are often considered the most important areas to be conserved in most national conservation policies, but many of them are not representative of national biodiversity. We assessed the biodiversity of vascular plants within and outside protected areas in South Korea by using a multi-response species dist...
Article
Full-text available
The study of crop origins has traditionally involved identifying geographic areas of high morphological diversity, sampling populations of wild progenitor species, and the archaeological retrieval of macroremains. Recent investigations have added identification of plant microremains (phytoliths, pollen, and starch grains), biochemical and molecular...
Article
AimModelling complex environmental and ecological processes over large geographic areas is challenging, particularly when basic research and model development for such processes has historically been at the local scale. Moving from local toward global analysis brings up numerous issues related to data processing, aggregation, tradeoffs between mode...
Article
Weather affects the severity of many plant diseases, and climate change is likely to alter patterns of crop disease severity. Evaluating possible future patterns can help focus crop breeding and disease management research. We examined the global effect of climate change on potato late blight, the disease that caused the Irish potato famine and sti...
Article
Full-text available
Austral summer frosts in the Andean highlands are ubiquitous throughout the crop cycle, causing yield losses. In spite of the existing warming trend, climate change models forecast high variability, including freezing temperatures. As the potato center of origin, the region has a rich biodiversity which includes a set of frost resistant genotypes....
Article
Species distribution modeling (SDM) links ecological theory of species–environment relationships with statistical learning methods and geospatial data to understand and predict the distributions of species and their habitats. Also called ecological niche modeling, SDM is widely used for biodiversity assessment and to predict the impacts of environm...
Article
We evaluated the use of the "DeNitrification DeComposition" (DNDC) model to estimate variation in N2O emissions from agriculture for large geographic areas, using maize production in the United States as an example. We address practical and methodological issues, including how much model spin-up time is necessary; whether to run the model in "site"...
Article
Full-text available
Endangered species conservation planning needs to consider the effects of future climate change. Species distribution models are commonly used to predict future shifts in habitat suitability. We evaluated the effects of climate change on the highly endangered mountain gorilla (Gorilla beringei beringei ) using a variety of modeling approaches, and...
Article
Full-text available
Viticulture will not cease in major wine-growing regions in response to climate change, because vineyard managers will not let that happen. Adaptation measures will be taken to permit continued cultivation of wine grapes. These adaptation measures can place major stress on water resources and freshwater ecosystems (1).