Mike Hobbins

University of Colorado Boulder | CUB · Cooperative Institute for Research in Environmental Sciences (CIRES)

Flash droughts are a recently recognized type of extreme event distinguished by sudden onset and rapid intensification of drought conditions with severe impacts. They unfold on subseasonal-to-seasonal timescales (weeks to months), presenting a new challenge for the surge of interest in improving subseasonal-to-seasonal prediction. Here we discuss e...

Many operational drought indices focus primarily on precipitation and temperature when depicting hydroclimatic anomalies, and this perspective can be augmented by analyses and products that reflect the evaporative dynamics of drought. The linkage between atmospheric evaporative demand E0 and actual evapotranspiration (ET) is leveraged in a new drou...

To fully attribute the variability of reference evapotranspiration to its drivers, a mean-value, second-moment uncertainty analysis is applied to a 30-year, CONUS-wide reanalysis of daily and annual tall-crop reference evapotranspiration as estimated by the ASCE Standardized Reference Evapotranspiration Equation driven by four variables from the No...

Precipitation, soil moisture, and air temperature are the most commonly used climate variables to monitor drought; however, other climatic factors such as solar radiation, wind speed, and humidity can be important drivers in the depletion of soil moisture and evolution and persistence of drought. This work assesses the Evaporative Demand Drought In...

Background Climate change will increase drought duration and severity in many regions around the world, including the Central Plains of North America. However, studies on drought-related health impacts are still sparse. This study aims to explore the potential associations between drought and all-cause mortality in Nebraska from 1980 to 2014. Meth...

Flash droughts can be distinguished by rapid intensification from near-normal soil moisture to drought conditions in a matter of weeks. Here, we provide the first characterisation of a climatology of flash drought across Australia using a suite of indices. The experiment is designed to capture a range of conditions related to drought: evaporative d...

‘Flash drought’ (FD) describes the rapid onset of drought on sub-seasonal times scales. It is of particular interest for agriculture as it can deplete soil moisture for crop growth in just a few weeks. To better understand the processes causing FD, we evaluate the importance of evaporative demand and precipitation by comparing three different droug...

In eastern Africa droughts can cause crop failure and lead to food insecurity. With increasing temperatures, there is an a priori assumption that droughts are becoming more severe. However, the link between droughts and climate change is not sufficiently understood. Here we investigate trends in long-term agricultural drought and the influence of i...

These proceedings contain the full-length papers, extended abstracts, and research abstracts of oral presentations and posters given at The Sixth ICRW focused on "working watersheds." These so-called watersheds and coastal systems provide a wide array of useful economic goods and services (e.g., agricultural products, urban development, recreation,...

In eastern Africa droughts can cause crop failure and lead to food insecurity. With increasing temperatures, there is an a priori assumption that droughts are becoming more severe, however, the link between droughts and climate change is not sufficiently understood. In the current study we focus on agricultural drought and the influence of high tem...

Relationships between drought indices and fire danger outputs are examined to (1) incorporate fire risk information into the National Integrated Drought Information System California–Nevada Drought Early Warning System and (2) provide a baseline analysis for application of drought indices into a fire risk management framework. We analyzed four drou...

The monitoring and forecasting of drought is undergoing a paradigm shift with regard to the treatment of evapotranspiration (ET), evaporative demand (E0), and the consideration of temperature impacts on drought in a changing climate. Previously, these have been poorly estimated by physically flawed parameterizations with detrimental effects on the...

The Famine Early Warning Systems Network (FEWS NET) team provides food insecurity outlooks for several developing countries in Africa, central Asia, and Central America. This study describes development of a new global reference evapotranspiration (ET0) seasonal reforecast and skill evaluation with a particular emphasis on the potential use of this...

Drought is a complex phenomenon manifested through interactions between biophysical and social factors. At the Wind River Indian Reservation (WRIR) in west-central Wyoming, water shortages have become increasingly common since the turn of the 21st century. Here we discuss the 2015 water year as an exemplar year, which was characterized by wetter-th...

Several studies have projected increases in drought severity, extent and duration in many parts of the world under climate change. We examine sources of uncertainty arising from the methodological choices for the assessment of future drought risk in the continental US (CONUS). One such uncertainty is in the climate models’ expression of evaporative...

Stations from the NOAA cooperative observer network with pan evaporation data used to extend the dataset originally compiled by Hobbins (2004). (DOCX)

Evapotranspiration is the transfer of moisture from sources at the surface into the atmosphere; evaporative demand is its maximum value assuming unlimited moisture availability and ambient atmospheric conditions. Despite evapotranspiration being an essential flux in the water balance at all scales and its importance to many sectors of human endeavo...

A novel CONUS-wide evaluation of reference evapotranspiration (ET0; a formulation of evaporative demand) anomalies is performed using the Climate Forecast System version 2 (CFSv2) reforecast data for 1982-2009. This evaluation was motivated by recent research showing ET0 anomalies can accurately represent drought through exploitation of the complem...

The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ETref) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ETref, which is essential for regional scale water resources mana...

This white paper focuses on the societal benefits and applications of satellite mapping of evapotranspiration (ET) and its use to address a wide range of water resource management challenges and information needs. It summarizes the findings, conclusions and recommendations from the participants of the 2015 Workshop on Evapotranspiration Mapping for...

California is in the midst of a historic drought in terms of both duration and severity, and the extreme moisture deficit has led to alarmingly low streamflow and reservoir levels since the last above average water year of 2011. While lack of precipitation is one cause of the depleted surface water, other factors such as record breaking warm temper...

We have developed a physically based, multi-scalar drought index—the Evaporative Demand Drought Index, or EDDI—that leverages the inter-relations of evaporative demand (E0) and actual evapotranspiration (ET) to improve the treatment of evaporative dynamics in drought monitoring and offer drought early warning. EDDI measures E0’s physical response t...

The North American Land Data Assimilation System project phase 2 (NLDAS-2) has run four land surface models for a 30-year (1979-2008) retrospective period. Land surface evapotranspiration (ET) is one of the most important model outputs from NLDAS-2 for investigating land-atmosphere interaction or to monitor agricultural drought. Here, we evaluate h...

Currently, NLDAS is an operational system that supports U.S. operational drought monitoring and seasonal hydrological prediction, in particular for the National Integrated Drought Information System, the U.S. Drought Monitor (USDM), and the NCEP Climate Prediction Center monthly drought briefings. Detailed information about NLDAS can be found at NO...

What is EDDI? EDDI, which stands for Evaporative Demand Drought Index, is a drought index that can serve as an indicator of both rapidly evolving "flash" droughts (developing over a few weeks) and sustained droughts (developing over months but lasting up to years). Why use EDDI? EDDI has been shown to offer early warning of drought stress relative...

The potential evapotranspiration (PET) that would occur with unlimited plant access to water is a central driver of simulated plant growth in many ecological models. PET is influenced by solar and longwave radiation, temperature, wind speed, and humidity, but it is often modeled as a function of temperature alone. This approach can cause biases in...

Concurrent with the trend of rising global average air temperature, there have been worldwide observations of a decline in pan evaporation over the last 30-50 years. This global phenomenon has since received much attention from the scientific community. Better interpretation of the long-term trend of pan evaporation (involving seasonal and inter-an...

Assessing climate change risk to municipal water supplies is often conducted by hydrologic modeling specific to local watersheds and infrastructure to ensure that outputs are compatible with existing planning frameworks and processes. This study leverages the modeling capacity of an operational National Weather Service River Forecast Center to expl...

To understand the sources of temporal and spatial variability of atmospheric evaporative demand across the conterminous United States (CONUS), a mean-value, second-moment uncertainty analysis is applied to a spatially distributed dataset of daily synthetic pan evaporation for 1980-2009. This evaporative demand measure is from the "PenPan" model, wh...

This research is a response to worldwide observations reporting a decline in pan evaporation over the last 30 to 50 years. We constructed an instrumented US Class A pan that replicates an operational pan at Canberra Airport in Australia. The aim of the experimental setup was to investigate the physics of pan evaporation under non-steady state condi...

Existing drought monitors rely heavily on precipitation (Prcp) and temperature (T) data to derive moisture fluxes at the surface, often using estimates of evaporative demand (Eo) based only on T to derive actual evapotranspiration (ET) from land surface models (LSMs). An example of this is the popular Palmer Drought Severity Index (PDSI). In the an...

The recent multi-year drought in the upper Colorado R. basin brought storage levels in the major reservoirs of the basin (Mead and Powell) to alarmingly low levels that raised national media attention. The conditions of the early 2000s combined with increasing water demand have brought greater scrutiny of forecasting and water management practices...

Due to the essentially unknowable nature of the distribution of soil and vegetative moisture at spatial scales useful to water managers and agriculturalists, hydrologists have long used the concept of evaporative demand to describe the upper limit of evapotranspiration. Formulations of evaporative demand have varied greatly in terms of their data r...

This study emerged from the declines in pan evaporation reported across many regions worldwide (Roderick et al., 2009a; Roderick et al., 2009b). Our aim is to fully investigate this phenomenon. We constructed an instrumented Class A pan at the Bureau of Meteorology field station at Canberra Airport in 2007 to study pan evaporation under non-steady...

The original and modified versions of the advection-aridity (AA) model of regional evapotranspiration are tested with data from the Solar and Meteorological Surface Observation Network (SAMSON). The resulting long-term mean annual evapotranspiration estimates are validated against water balances of 25 watersheds that are minimally affected by human...

Pan evaporation is just that – it is the evaporation rate of water from a small dish located at the ground-surface. Pan evaporation is a measure of the evaporative demand over terrestrial surfaces. Declines in pan evaporation have now been reported in many regions of the world. The trends vary from one pan to the next, but when averaged over many p...

Declines in pan evaporation have been reported across the USA, former Soviet Union, India, China, Australia, New Zealand and Canada, among other places. The trend is large – approximately an order of magnitude larger than model-based estimates of top of the atmosphere radiative forcing. The pan evaporation trend also has a different sign (i.e. decl...

In contrast to the Wentz et al (2007) result for the global oceans, terrestrial site-based studies show substantial declines in near-surface wind speeds over the last 30 to 50 years (Roderick et al. 2007). That decline impacts evaporative demand of the terrestrial hydrological cycle. Wind speed is difficult to measure so how do we know that these t...

Available water supply across the contiguous 48 states was estimated as precipitation minus evapotranspiration using data for the period 1953-1994. Precipitation estimates were taken from the Parameter-Elevation Regressions on Independent Slopes Model (PRISM). Evapotranspiration was estimated using two models, the Advection-Aridity model and the Zh...

1 ] We examine the effects of two different parameterizations of potential evaporation on long-term trends in soil moisture, evaporative flux and runoff simulated by the water balance model underlying the Palmer Drought Severity Index. The first, traditional parameterization is based on air temperature alone. The second parameterization is derived...

Evaporative demand is routinely measured using the evaporation of water from standardised pans. The most common are Class A pans: they are metal dishes 4 feet in diameter and 10 inches deep sitting on a wooden platform. Because of the practical importance in agriculture and engineering, there is a wealth of pan evaporation data. Analysis has shown...

Evaporative demand, measured by pan evaporation, has declined in many regions over the last several decades. It is important to understand why. Here we use a generic physical model based on mass and energy balances to attribute pan evaporation changes to changes in radiation, temperature, humidity and wind speed. We tested the approach at 41 Austra...

A paradigm is developing that holds global warming responsible for drying of mid-latitude continental interiors, with a consequent increase in drought exposure. To a large degree, such predictions rest on using rainfall and potential evapotranspiration (ETp) to compute the Palmer Drought Severity Index (PDSI). In its standard form, the PDSI uses th...

[1] Using independent observations of actual and potential evapotranspiration at a wide range of spatial scales, we provide direct observational evidence of the complementary relationship in regional evapotranspiration hypothesized by Bouchet in 1963. Bouchet proposed that, for large homogeneous surfaces with minimal advection of heat and moisture,...

The quantity of water originating on each 5-km by 5-km cell across the contiguous 48 states was estimated as precipitation minus evapotranspiration (ET) using data for the period 1953-94. Precipitation was estimated using the model PRISM. ET was estimated using two models, the Advection-Aridity model and the so-called Zhang model. These models were...

Long-term observations of pan evaporation and water budget-derived evapotranspiration across the conterminous United States provide the first observational evidence supporting the hypothesis of a complementary relationship in regional evapotranspiration, in terms both of the evaporation rates themselves and of long-term trends in their component dy...

Pan evaporation (ETpan) has decreased at 64% of pans in the conterminous U.S. over the past half-century. Comparing trends in ETpan and water budget-derived actual evapotranspiration (ET*a), we observe the so-called “Pan Evaporation Paradox,” which we confirm is no more than a manifestation of the complementarity between actual evapotranspiration (...

Our aim is to develop a long-term, high resolution net radiation data set that accounts for the effects of local topography that confound simpler analyses of the shortwave radiative balance in rugged terrain; such a dataset may then be used in direct observations of the effects of long-term change and variability in the solar radiation input to the...

https://babel.hathitrust.org/cgi/pt?id=umn.31951d02835525c&view=1up&seq=21

Two implementations of the complementary relationship hypothesis for regional evapotranspiration, the Complementary Relationship Areal Evapotranspiration (CRAE) model and the Advection-Aridity (AA) model, are evaluated against independent estimates of regional evapotranspiration derived from long-term, large-scale water balances (1962–1988) for 120...

Long-term monthly evapotranspiration estimates from Brutsaert and Stricker's Advection-Aridity model were compared with independent estimates of evapotranspiration derived from long-term water balances for 139 undisturbed basins across the conterminous United States. On an average annual basis for the period 1962-1988 the original model, which uses...

The hypothesis of a complementary relationship in regional evapotranspiration allows for estimation of actual evapotranspiration on a regional scale by simple, physically based models that take into account feedbacks in land surface-atmosphere dynamics. A regional, seasonal Advection-Aridity model is used to create a monthly time-series of actual e...

The hypothesis of a complementary relationship in regional evapotranspiration allows for estimation of actual evapotranspiration on a regional scale by simple, physically based models that take into account feedbacks in land surface-atmosphere dynamics. A regional, seasonal Advection-Aridity model is used to create a monthly time-series of actual e...

Two implementations of the complementary relationship hypothesis for regional evapotranspiration—the Complementary Relationship Areal Evapotranspiration (CRAE) model and the Advection-aridity (AA) model—are evaluated against independent estimates of regional evapotranspiration derived from long-term (WY 1962–1988), large-scale water balances for 13...

Results from Brutsaert and Stricker's Advection-aridity evapotranspiration model were compared at the monthly time step with independent estimates of evapotranspiration derived from water balances for 139 large, undisturbed basins across the conterminous U.S. On an average annual basis for the period 1962-1988, the original model, which uses a Penm...