Anthropogenic land-use change in the North American tall grass-short grass transition and modification of near-surface hydrologic cycle

During the 19th and 20th centuries, the landscape of the North American Great Plains was rapidly modified from natural grasslands to agricultural farmlands. These changes affected much of the continent with potential impacts in grasslands equal to deforestation elsewhere. Therefore, the resulting impacts on weather and climate should be studied. In this study, a soil water balance model is applied for 3 land uses at 3 locations. These locations are representative of the east to west declining precipitation gradient of the Great Plains. It was found, in McCook, Nebraska, for example, that annual total evapotranspiration for irrigated maize is 36% higher compared to natural grass. This accounts for an additional 50 million m3 of water evapotranspired into the atmosphere from an area of 19 000 ha during the growing season. In some instances, Clay Center, Nebraska, and the vicinity evapotranspired nearly 100 million m3 additional water (compared to a grass covered surface) from irrigated maize during the growing season. Compared to grass, irrigated maize farming elevated soil water in the soil profile, while rainfed maize lowered soil water. This study shows that intensity of the response of soil water distribution in the root zone is a function of vegetation cover and soil physical properties

An Analysis of Simulated Long-Term Soil Moisture Data for Three Land Uses under Contrasting Hydroclimatic Conditions in the Northern Great Plains

Soil moisture (SM) plays an important role in land surface and atmosphere interactions. It modifies energy balance near the surface and the rate of water cycling between land and atmosphere. The lack of observed SM data prohibits understanding of SM variations at climate scales under varying land uses. However, with simulation models it is possible to develop a long-term SM dataset and study these issues. In this paper a water balance model is used to provide a quantitative assessment of SM climatologies for three land uses, namely, irrigated corn, rain-fed corn, and grass, grown under three hydroclimatic regimes in Nebraska. These regimes are stops along an east–west decreasing precipitation gradient of the Great Plains. The simulated SM climatologies are provided for the root zone as a whole and for the five layers of the soil profile to a depth of 1.2 m. As expected, the soil water content in the root zone of irrigated corn was higher than rainfed corn or grass. The lowest levels of soil water depletion were found under rain-fed corn cultivation due to its complete reliance on naturally available SM. The annual total evapotranspiration (ET) was 34% and 36% higher for irrigated corn than for rain-fed corn and grass, respectively. The study suggests that due to interannual variability the SM variability is higher for deeper depths, as compared to near-surface depths. Growing season SM depletion and prevailing soil water content at various depths of the soil profile varies with crops, soils, and prevailing hydroclimatic conditions. The results show that land use affects the magnitude of SM variability at all time scales. At a daily temporal scale, SM variability is less under irrigated land use and sharply increases under rain-fed land uses. At the monthly scale, SM variability largely follows the trend of the daily time scale. Year-to-year SM variability is significant. Extremely dry or wet conditions enhance and reduce, respectively, the forcing of land use on SM variability at an annual time scale. Thus, large-scale interannual climate variations and land use jointly affect SM variability at this scale

Influence of Karst Landscape on Planetary Boundary Layer Atmosphere: A Weather Research and Forecasting (WRF) Model–Based Investigation

Karst hydrology provides a unique set of surface and subsurface hydrological components that affect soil moisture variability. Over karst topography, surface moisture moves rapidly below ground via sink holes, vertical shafts, and sinking streams, reducing surface runoff and moisture infiltration into the soil. In addition, subsurface cave blockage or rapid snowmelt over karst can lead to surface flooding. Moreover, regions dominated by karst may exhibit either drier or wetter soils when compared to nonkarst landscape. However, because of the lack of both observational soil moisture datasets to initialize simulations and regional land surface models (LSMs) that include explicit karst hydrological processes, the impact of karst on atmospheric processes is not fully understood. Therefore, the purpose of this study was to investigate the importance of karst hydrology on planetary boundary layer (PBL) atmosphere using the Weather Research and Forecasting Model (WRF). This research is a first attempt to identify the impacts of karst on PBL. To model the influence of karst hydrology on atmospheric processes, soil moisture was modified systematically over the Western Kentucky Pennyroyal Karst (WKYPK) region to produce an ensemble of dry and wet anomaly experiments. Simulations were conducted for both frontal- and nonfrontal-based convection. For the dry ensemble, cloud cover was both diminished downwind of karst because of reduced atmospheric moisture and enhanced slightly upwind as moist air moved into a region of increased convection compared to control simulations (CTRL). Moreover, sensible (latent) heat flux and PBL heights were increased (decreased) compared to CTRL. In addition, the wet ensemble experiments reduced PBL heights and sensible heat flux and increased cloud cover over karst compared to CTRL. Other changes were noted in equivalent potential temperature (θe) and vertical motions and development of new mesoscale circulation cells with alterations in soil moisture over WKYPK. Finally, the location of simulated rainfall patterns were altered by both dry and wet ensembles with the greatest sensitivity to simulated rainfall occurring during weakly forced or nonfrontal cases. Simulated rainfall for the dry ensemble was more similar to the North American Regional Reanalysis (NARR) than CTRL for the nonfrontal case. Furthermore, the initial state of the atmosphere and convective triggers were found to either enhance or diminish simulated atmospheric responses

Drought and Land-Cover Conditions in the Great Plains

Land–atmosphere interactions play a critical role in the Earth system, and a better understanding of these interactions could improve weather and climate models. The interaction among drought, vegetation productivity, and land cover is of particular significance. In a semiarid environment, such as the U.S. Great Plains, droughts can have a large influence on the productivity of agriculture and grasslands, with serious environmental and economic impacts. Here, we used the vegetation drought response index (VegDRI) drought indicator to investigate the response of vegetation to weather and climate for landcover types in the Great Plains in the United States from 1989 to 2012. We found that analysis that focused on land-cover types within ecoregion divisions provided substantially more and land-cover-based detail on the timing and intensity of drought than did summarizing across the entire Great Plains region. In the northern Great Plains, VegDRI measured more frequent drought impacts on vegetation in the western ecoregions than in the eastern ecoregions. Across the ecoregions of the Great Plains, drought impacts on vegetation were more commonly found in grassland than in cropland. For example, in the ‘‘Northwestern Great Plains’’ ecoregion (which encompasses areas of Montana, Wyoming, North Dakota, South Dakota, and Nebraska), grassland and nonirrigated cropland were observed in VegDRI to have historical fractional drought coverages in the growing season of 17% and 11%, respectively

The Prairie Post Quarterly Newsletter of the High Plains Regional Climate Center- January 2019

Inside this issue: Message from the director........................................1 Staff spotlight...........................1 Year in review............................2 Drought THIRA toolkit...........3 Product highlight....................4 Update on regional climate conditions..................................4 Other HPRCC news.................5 Recent and upcoming travel and activities.............................

The Prairie Post Quarterly Newsletter of the High Plains Regional Climate Center- October 2019

Inside this issue: Message from the director........................................1 Staff spotlight...........................1 Workshops focus on climate services in Kansas....................2 Research highlights................3 AMS Annual Meeting.............3 Update on regional climate conditions..................................4 New ACIS Climate Summary Maps available..........................5 Track precipitation with CLIMOD.......................................5 Recent and upcoming travel and activities.............................

Increase in Near-Surface Atmospheric Moisture Content due to Land Use Changes: Evidence from the Observed Dewpoint Temperature Data

Land use change can significantly affect root zone soil moisture, surface energy balance, and near-surface atmospheric temperature and moisture content. During the second half of the twentieth century, portions of the North American Great Plains have experienced extensive introduction of irrigated agriculture. It is expected that land use change from natural grass to irrigated land use would significantly increase nearsurface atmospheric moisture content. Modeling studies have already shown an enhanced rate of evapotranspiration from the irrigated areas. The present study analyzes observed dewpoint temperature (Td) to assess the affect of irrigated land use on near-surface atmospheric moisture content. This investigation provides a unique opportunity to use long-term (1982–2003) mesoscale Td data from the Automated Weather Data Network of the high plains. Long-term daily Td data from 6 nonirrigated and 11 irrigated locations have been analyzed. Daily time series were developed from the hourly data. The length of time series was the primary factor in selection of these stations. Results suggest increase in growing-season Td over irrigated areas. For example, average growing-season Td due to irrigation can be up to 1.56°C higher relative to nonirrigated land uses. It is also found that Td for individual growing-season month at irrigated locations can be increased up to 2.17°C by irrigation. Based on the results, it is concluded that the land use change in the Great Plains has modified near-surface moistness

The Prairie Post Quarterly Newsletter of the High Plains Regional Climate Center- October 2018

Inside this issue: Message from the interim director........................................1 Staff spotlight...........................1 ACIS GIS portal release..........2 ACIS maps enhancement.....3 Product highlight....................4 Update on regional climate conditions..................................4 Update on tribal engagement............................................. 5 Recent and upcoming travel and activities.............................

Growing Season Air mass Equivalent Temperature (TE) in the East Central USA

Equivalent temperature (TE), which incorporates both dry (surface air temperature, T) and moist heat content associated with atmospheric moisture, is a better indicator of overall atmospheric heat content compared to T alone. This paper investigates the impacts of different types of air masses on TE during the growing season (April–September). The study used data from the Kentucky Mesonet for this purpose. The growing season was divided into early (April–May), mid (June–July), and late (August–September). Analysis suggests that TE for moist tropical (MT) air mass was as high as 61 and 81 C for the early and mid-growing season, respectively. Further analysis suggests that TE for different parts of the growing seasons were statistically significantly different from each other. In addition, TE for different air masses was also statistically significantly different from each other. The v between TE and T (i.e. TE-T) is smaller under dry atmospheric conditions but larger under moist conditions. For example, in Barren County, the lowest difference (20–10 C) was 10 C. It was reported on 18 April 2010, a dry weather day. On the other hand, the highest difference for this site was 48 C and was reported on 11 August 2010, a humid day

The Prairie Post Quarterly Newsletter of the High Plains Regional Climate Center- April 2019

Inside this issue: Message from the director........................................1 Staff spotlight...........................1 Climate4Cities.......................2-3 Product highlight....................4 Update on regional climate conditions..................................4 THREDDS workshop...............5 AASC webinar...........................5 Recent and upcoming travel and activities.............................