High Surface Soil Moisture Research Articles

Climate‐change refugia in boreal North America: what, where, and for how long?

The vast boreal biome plays an important role in the global carbon cycle but is experiencing particularly rapid climate warming, threatening the integrity of valued ecosystems and their component species. We developed a framework and taxonomy to identify climate‐change refugia potential in the North American boreal region, summarizing current knowledge regarding mechanisms, geographic distribution, and landscape indicators. While “terrain‐mediated” refugia will mostly be limited to coastal and mountain regions, the ecological inertia (resistance to external fluctuations) contained in some boreal ecosystems may provide more extensive buffering against climate change, resulting in “ecosystem‐protected” refugia. A notable example is boreal peatlands, which can retain high surface soil moisture and water tables even in the face of drought. Refugia from wildfire are also especially important in the boreal region, which is characterized by active disturbance regimes. Our framework will help identify areas of high refugia potential, and inform ecosystem management and conservation planning in light of climate change.

A Soil Moisture Spatial and Temporal Resolution Improving Algorithm Based on Multi-Source Remote Sensing Data and GRNN Model

Surface soil moisture (SM) plays an essential role in the water and energy balance between the land surface and the atmosphere. Low spatio-temporal resolution, about 25–40 km and 2–3 days, of the commonly used global microwave SM products limits their application at regional scales. In this study, we developed an algorithm to improve the SM spatio-temporal resolution using multi-source remote sensing data and a machine-learning model named the General Regression Neural Network (GRNN). First, six high spatial resolution input variables, including Land Surface Temperature (LST), Normalized Difference Vegetation Index (NDVI), albedo, Digital Elevation Model (DEM), Longitude (Lon) and Latitude (Lat), were selected and gap-filled to obtain high spatio-temporal resolution inputs. Then, the GRNN was trained at a low spatio-temporal resolution to obtain the relationship between SM and input variables. Finally, the trained GRNN was driven by the high spatio-temporal resolution input variables to obtain high spatio-temporal resolution SM. We used the Fengyun-3B (FY-3B) SM over the Tibetan Plateau (TP) to test the algorithm. The results show that the algorithm could successfully improve the spatio-temporal resolution of FY-3B SM from 0.25° and 2–3 days to 0.05° and 1-day over the TP. The improved SM is consistent with the original product in terms of both spatial distribution and temporal variation. The high spatio-temporal resolution SM allows a better understanding of the diurnal and seasonal variations of SM at the regional scale, consequently enhancing ecological and hydrological applications, especially under climate change.

SMOS disaggregated soil moisture product at 1 km resolution: Processor overview and first validation results

Abstract The SMOS (Soil Moisture and Ocean Salinity) mission provides surface soil moisture (SM) maps at a mean resolution of ~ 50 km. However, agricultural applications (irrigation, crop monitoring) and some hydrological applications (floods and modeling of small basins) require higher resolution SM information. In order to overcome this spatial mismatch, a disaggregation algorithm called Disaggregation based on Physical And Theoretical scale Change (DISPATCH) combines higher-resolution data from optical/thermal sensors with the SM retrieved from microwave sensors like SMOS, producing higher-resolution SM as the output. A DISPATCH-based processor has been implemented for the whole globe (emerged lands) in the Centre Aval de Traitement des Donnees SMOS (CATDS), the French data processing center for SMOS Level 3 products. This new CATDS Level-4 Disaggregation processor (C4DIS) generates SM maps at 1 km resolution. This paper provides an overview of the C4DIS architecture, algorithms and output products. Differences with the original DISPATCH prototype are explained and major processing parameters are presented. The C4DIS SM product is compared against L3 and in situ SM data during a one year period over the Murrumbidgee catchment and the Yanco area (Australia), and during a four and a half year period over the Little Washita and the Walnut Gulch watersheds (USA). The four validation areas represent highly contrasting climate regions with different landscape properties. According to this analysis, the C4DIS SM product improves the spatio-temporal correlation with in situ measurements in the semi-arid regions with substantial SM spatial variability mainly driven by precipitation and irrigation. In sub-humid regions like the Little Washita watershed, the performance of the algorithm is poor except for summer, as result of the weak moisture-evaporation coupling. Disaggregated products do not succeed to have and additional benefit in the Walnut Gulch watershed, which is also semi-arid but with well-drained soils that are likely to cancel the spatial contrast needed by DISPATCH. Although further validation studies are still needed to better assess the performance of DISPATCH in a range of surface and atmospheric conditions, the new C4DIS product is expected to provide satisfying results over regions having medium to high SM spatial variability.

Effects of invasive knapweed (Centaurea stoebesubsp.micranthos) on a threatened native thistle (Cirsium pitcheri) vary with environment and life stage

We examined the type and magnitude of invasive plant (Centaurea stoebe subsp. micranthos (Gugler) Hayek) effects on the demographic parameters of a rare plant (Cirsium pitcheri Torr. & A.Gray), using two seed addition experiments with three treatments in two dune habitats — lakeshore linear dunes and high perched dunes on Lake Michigan, USA. Treatments were near Centaurea stoebe subsp. micranthos, near a native plant, or in the open. Seedling emergence, establishment, and juvenile survivorship were significantly higher on perched dunes, with higher surface soil moisture, than on lakeshore dunes. Treatment effects varied significantly with habitat and life stage. Seedling establishment decreased near Centaurea stoebe subsp. micranthos on lakeshore dunes, but increased near any neighbor on perched dunes. However, juvenile survival was significantly lower near Centaurea stoebe. subsp. micranthos in both habitats. The probability of reaching the adult flowering stage was much lower, and occurred later, for plants near Centaurea stoebe subsp. micranthos, especially on lakeshore dunes. Thus, Centaurea stoebe subsp. micranthos had a strong negative effect on establishment, survival, and flowering of Cirsium pitcheri, but interaction intensity varied with habitat and life stage. The results suggest that coupling seed addition with watering and invasive plant removal could bolster populations of this rare endemic plant.

Local topography and erosion rate control regolith thickness along a ridgeline in the Sierra Nevada, California

AbstractThe ridgelines of mountain ranges are a source of geomorphic information unadulterated by the arrival of sediment from upslope. Studies along ridgecrests, therefore, can help identify and isolate the controls on important regolith properties such as thickness and texture. A 1.5 km section of ridgeline in the Sierra Nevada (CA) with a tenfold decrease in erosion rate (inferred from ridgetop convexity) provided an opportunity to conduct a high‐resolution survey of regolith properties and investigate their controls. We found that regolith along the most quickly eroding section of the ridge was the rockiest and had the lowest clay concentrations. Furthermore, a general increase in regolith thickness with a slowing of erosion rate was accompanied by an increase in biomass, changes in vegetation community, broader ridgeline profiles, and an apparent increase in total available moisture. The greatest source of variation in regolith thickness at the 10–100 m scale, however, was the local topography along the ridgeline, with the deepest regolith in the saddles and the thinnest on the knobs. Because regolith in the saddles had higher surface soil moisture than the knobs, we conclude that the hydrological conditions primarily driven by local topography (i.e. rapid vs. slow drainage and water‐storage potential) provide the fundamental controls on regolith thickness through feedbacks incorporating physical weathering by the biota and chemical weathering. Moreover, because the ridgeline saddles are the uppermost extensions of first‐order valleys, we propose that the fluvial network affects regolith properties in the furthest reaches of the watershed. Copyright © 2015 John Wiley & Sons, Ltd.

Evapotranspiration and Crop Coefficients for Seepage-Irrigated Watermelon with Plastic Mulch in a Sub-Tropical Region

<abstract><title><italic>Abstract.</italic></title> The crop coefficient (K_c) method is the most widely used method for computing crop evapotranspiration (ET_c) and relies on selecting a representative K_c value for a specific production system, soil, and climate. Literature-based (e.g., FAO-56) K_c values, used in the absence of local K_c, can lead to erroneous ET_c estimates. This error becomes considerably high when the standard K_c values from the open-field production systems are applied to plastic mulch production systems with seepage irrigation that results in shallow water table conditions. A three-year study (2003-2005) was conducted with two large drainage lysimeters (length = 4.87 m, width = 3.65 m, and depth = 1.37 m) to quantify ET_c and K_c for seepage-irrigated watermelon under plastic mulch in sub-tropical Florida. The seasonal ET_c varied from 344 to 422 mm, with an average of 373 mm. The K_c values for initial, development, mid-season, and late stages were 0.64, 1.00, 1.28, and 1.15, respectively, and were statistically higher than the values reported in the literature, including FAO-56. The initial K_c especially was greater than the literature values due to low plant cover and high surface soil moisture in the row-middle areas at the beginning of the season resulting from frequent rainfall and shallow water table. To adjust K_c for the effect of variable rainfall wetting on evaporation during the initial stage, a multivariate regression model (r² = 0.74) was developed as a function of rainfall and solar radiation. Use of literature-based K_c values resulted in underestimation of seepage-irrigated ET_c by 26% to 43%; the 26% underestimation was from a comparison using the same lysimeter setup and seasons but with drip (surface) irrigation. Such large differences, not reported earlier, highlight the importance of developing local K_c for a specific irrigation method, climate, and production system. Regression models (r² = 0.96) were developed for predicting K_c as functions of time and growing degree days. With approximately 65,000 ha of vegetables grown under seepage irrigation in Florida, there is a need for developing local K_c values for irrigation management and water allocations. Scaling up the errors in water use from literature-based K_c values to Florida’s seepage-irrigated vegetable lands for one season per year showed errors of 25 to 42 million m³ of water. This error accounts for 15% to 25% of annual rainfall and is likely to be much higher for dual cropping systems within a year. The extent of errors and related effects on watershed water balances highlight the need for similar studies for other seepage-irrigated mulched crops.

Hydroclimatology of the 2008 Midwest floods

The late spring/early summer flooding that occurred in the American Midwest between May and June 2008 resulted from a combination of large‐scale atmospheric circulation patterns that supported a steady influx of moisture into the area. A low pressure system centered over the central‐western United States steered a strong jet and associated storms along its eastern edge from the west to southwest and an anomalously strong Great Plains Low Level Jet brought continuous warm and moist air into the area from the Gulf of Mexico into the area. We examine and quantify here the impact these circulation patterns had on the hydroclimatology of the Midwest highlighting the magnitude, frequency, geographic distribution, and temporal evolution of precipitation that ultimately magnified the flooding. Historical precipitation records were used to assess the regional rainfall characteristics at various geographic and time scales. Five distinct hydroclimatic characteristics contributed to the definition of the 2008 flood including persistent high surface soil moisture conditions prior to flooding exasperated by anomalously high rainfall, extreme rainfall totals covering extensive areas, increased frequency of shorter‐term, smaller‐magnitude events, persistent multiday heavy precipitation events, and extreme flood‐producing rain storms. The major flooding lasted for approximately 24 days and most greatly impacted the state of Iowa, southern Wisconsin, and central Indiana. Its occurrence during the May–June period makes the event especially unusual for this region.

Cultivation of a perennial grass for bioenergy on a boreal organic soil – carbon sink or source?

AbstractThe area under the cultivation of perennial bioenergy crops on organic soils in the northern countries is fast increasing. To understand the impact of reed canary grass (RCG, Phalaris arundinaceae L.) cultivation on the carbon dioxide (CO2) balance of an organic soil, net ecosystem CO2 exchange (NEE) was measured for four years in a RCG cultivated cutover peatland in eastern Finland using the eddy covariance technique. There were striking differences among the years in the annual precipitation. The annual precipitation was higher during 2004 and 2007 and lower during 2005 and 2006 than the 1971–2000 regional mean. During wet growing seasons, moderate temperatures, high surface soil moisture and low evaporative demand favoured high CO2 uptake. During dry seasons, owing to soil moisture and atmospheric stress, photosynthetic activity was severely restricted. The CO2 uptake [gross primary productivity (GPP)] was positively correlated with soil moisture, air temperature and inversely with vapour pressure deficit. Total ecosystem respiration (TER) increased with increasing soil temperature but decreased with increasing soil moisture. The relative responses of GPP and TER to moisture stress were different. While changes in TER for a given change in soil moisture were moderate, variations in GPP were drastic. Also, the seasonal variations in TER were not as conspicuous as those in GPP implying that GPP is the primary regulator of the interannual variability in NEE in this ecosystem. The ecosystem accumulated a total of 398 g C m−2 from the beginning of 2004 until the end of 2007. It retained some carbon during a wet year such as 2004 even after accounting for the loss of carbon in the form of harvested biomass. Based on this CO2 balance analysis, RCG cultivation is found to be a promising after‐use option on an organic soil.

A study of land surface processes using land surface models over the Little River Experimental Watershed, Georgia

Three different land surface models (Hydrological improvements to the Simplified version of the Simple Biosphere model (HySSiB), Noah model, and Community Land Model (CLM)) were simulated on the NASA Goddard Space Flight Center's Land Information System platform at 1‐km resolution over the Little River Experimental Watershed, Georgia, and the simulated results were analyzed to address the local‐scale land‐atmosphere processes. All the three models simulated the soil moisture in space and time realistically. The Noah model produced higher soil moisture whereas the CLM got lower soil moisture with many dry down phases. CLM and HySSiB models were oversensitive to the atmospheric events. Different vertical discretizations of the model layers affected the soil moisture results in all the three models. The arithmetic model ensemble mean soil moisture performed reasonably well even at individual in‐situ measurement sites. We found that different model schemes partitioned the incoming water and energy differently and hence produced different results for the water and energy budget parameters. In CLM, the energy and water budget parameters were very closely connected to the soil moisture (e.g., evaporation, latent, and sensible heat) change. HySSiB produced very high surface runoff and very low subsurface runoff. The Noah model did not produce much surface and subsurface runoff resulting in high surface soil moisture. We did not find much variability in Noah latent heat, sensible heat, and ground heat fluxes. From soil moisture data assimilation point of view, the mean bias removed Noah soil moisture was found to be better than other data sets.

Comparison of ERS-2 SAR and Landsat TM imagery for monitoring agricultural crop and soil conditions

Studies over the past 25 years have shown that measurements of surface reflectance and temperature (termed optical remote sensing) are useful for monitoring crop and soil conditions. Far less attention has been given to the use of radar imagery, even though synthetic aperture radar (SAR) systems have the advantages of cloud penetration, all-weather coverage, high spatial resolution, day/night acquisitions, and signal independence of the solar illumination angle. In this study, we obtained coincident optical and SAR images of an agricultural area to investigate the use of SAR imagery for farm management. The optical and SAR data were normalized to indices ranging from 0 to 1 based on the meteorological conditions and sun/sensor geometry for each date to allow temporal analysis. Using optical images to interpret the response of SAR backscatter ( σ o) to soil and plant conditions, we found that SAR σ o was sensitive to variations in field tillage, surface soil moisture, vegetation density, and plant litter. In an investigation of the relation between SAR σ o and soil surface roughness, the optical data were used for two purposes: (1) to filter the SAR images to eliminate fields with substantial vegetation cover and/or high surface soil moisture conditions, and (2) to evaluate the results of the investigation. For dry, bare soil fields, there was a significant correlation ( r 2=.67) between normalized SAR σ o and near-infrared (NIR) reflectance, due to the sensitivity of both measurements to surface roughness. Recognizing the limitations of optical remote sensing data due to cloud interference and atmospheric attenuation, the findings of this study encourage further studies of SAR imagery for crop and soil assessment.

Grizzly Bears and Resource-Extraction Industries: Effects of Roads on Behaviour, Habitat Use and Demography

In spring of 2010-2011, an experiment with treatments on soil water stress and sowing by stages of spring maize (Zea mays) was conducted in the central Jilin Province. The responses of maize emergence rate and yield to soil water stress were analyzed, and the assessment models of the emergence rate and reduction of yield caused by drought were established based on meteorological conditions. The results showed that during the study period, the relationship between maize emergence rate or per unit yield, and the soil moisture in 0-20 cm layer or soil available water content presented a significant quadratic function. The emergence rate and yield increased with the higher surface soil moisture, while decreased obviously under the drought condition. The emergence rate and yield were higher in the conditions of soil moisture in the range of 22%-24% or soil available water content in 50-65 mm, while the emergence rate and yield decreased obviously with the soil moisture less than 19% or available water content less than 35 mm. The soil moisture decreased 1% each, along with the emergence rate decreased by about 6% , and the yield decreased by about 7%. The soil available water content decreased by 10 mm, along with the emergence rate and yield decreased by about 13% and 14%, respectively. The indicators and models in this article could be applied to assessment and prediction of maize emergence rate and the reduction of yield caused by drought.

Surface Soil Moisture within a Watershed—Variations, Factors Influencing, and Relationship to Surface Runoff

AbstractSurface soil moisture was measured within the upper 15 cm using neutron‐scattering equipment on six soil series within a 57.8‐ha Pennsylvania watershed during the 19 May to 11 Nov. 1971 period. Surface soil moisture was responsive to individual storm events, showed discernible seasonal trends, and displayed larger fluctuations at higher moisture levels than at lower moisture levels. An analysis of variance showed that well‐drained soils had significantly different surface soil moisture levels than the more poorly drained soils and could be grouped into a hydrologic unit distinct from the more poorly drained soils. Surface soil moisture measurements along parallel transects approximately perpendicular to the slope contours showed high surface soil moisture contents proximal to the stream indicating that these areas contribute more to surface runoff in a shorter period of time than areas distant from the stream channel. Multiple regression equations using pan evaporation and surface soil moisture for each soil series were used to show the relative importance of the internal soil drainage class in predicting surface runoff.

Nitrogen Fixation by Soybeans as Influenced by Inoculum Placement: Greenhouse Studies1

AbstractMaximum summer surface soil temperatures in many areas greatly exceed the optimum temperature for symbiotic N fixation by legumes. Formation of nodules on roots deep in the soil may enhance N fixation because of reduced extremes in soil temperature and moisture. The purpose of the study was to determine whether nodule position could be controlled by inoculum placement and the effect of surface soil moisture on N fixation by such nodules.Soybeans (Glycine max (L.) Merr.) were grown in a greenhouse at Experiment, Georgia, in plastic pots containing preplaced rhizobial inoculum and 1.5 mg molybdenum at 15, 100, and 200 mm below the soil surface. High (90% field capacity) and low (air‐dry) surface soil moisture treatments were also included. Two experiments were conducted, one at moderate and the other at relatively high greenhouse temperatures (27 to 30 C and 37 to 41 C daily maxima, respectively). In all treatments, inoculation depth strongly influenced the pattern of nodule development with most of the nodular tissue forming on roots at or near the depth of inoculation. At moderate greenhouse temperatures, neither inoculation depth nor surface soil moisture affected the amount of N fixed. At relatively high greenhouse temperatures, plants in the low surface soil moisture treatments fixed less than 25% of the N fixed by those in the high surface soil moisture treatments at the 15 mm inoculation depth. A decrease in N fixation at the deeper inoculation depths was also observed at the higher greenhouse temperatures.