Robert R. Gillies

A method to make use of thermal infrared temperature and NDVI measurements to infer surface soil water content and fractional vegetation cover

Abstract A unique relationship between the surface soil moisture availability and the radiant temperature does not exist in the presence of variable vegetation cover. To overcome this ambiguity, the authors present a method which couples a Soil‐Vegetation‐Atmosphere‐Transfer (SVAT) model to satellite derived measurements of surface radiant temperature and Normalized Vegetation Difference Index (NDVI) to ascertain surface soil moisture availability and fractional vegetation cover. Application of the technique is demonstrated for an agricultural area in a Pennsylvania watershed. Results of surface soil moisture availability and fractional vegetation cover are qualitatively realistic but the distribution of soil moisture availability is questionable at high fractional vegetation amounts.

Thermal Remote Sensing of Surface Soil Water Content with Partial Vegetation Cover for Incorporation into Climate Models

Abstract This study outlines a method for the estimation of regional patterns of surface moisture availability (M0) and fractional vegetation (Fr) in the presence of spatially variable vegetation cover. The method requires relating variations in satellite-derived (NOAA, Advanced Very High Resolution Radiometer) surface radiant temperature to a vegetation index (computed from satellite visible and near-infrared data) while coupling this association to an inverse modeling scheme. More than merely furnishing surface soil moisture values, the method constitutes a new conceptual and practical approach for combining thermal infrared and vegetation index measurements for incorporating the derived values of M0 into hydrologic and atmospheric prediction models. Application of the technique is demonstrated for a region in and around the city of Newcastle upon Tyne situated in the northeast of England. A regional estimate of M0 is derived and is probably good for fractional vegetation cover up to 80% before errors i...

An assessment of satellite remotely-sensed land cover parameters in quantitatively describing the climatic effect of urbanization

The regional-scale climatic impact of urbanization is examined using two land cover parameters, fractional vegetation cover (Fr) and surface moisture availability (M0). The parameters are hypothesized to decrease as surface radiant temperature (T0) increases, forced by vegetation removal and the introduction of non-transpiring, reduced evaporating urban surfaces. Fr and M0 were derived from vegetation index and T0 data computed from the Advanced Very High Resolution Radiometer (AVHRR), and then correlated to a percentage of urban land cover obtained from a supervised classification of Landsat TM imagery. Data from 1985 through 1994 for an area near State College, PA, USA, was utilized. Urban land cover change (at the rate of 3 per cent perkm2 per year) was statistically significant when related to a decrease in normalized values of Fr and increase in normalized values of T0. The relationship between urbanization and M0, however, was ill-defined due to variations in the composition of urban vegetation. Fro...

An interpretation of methodologies for indirect measurement of soil water content

Using a new technique referred to as the triangle method, surface soil water content and fractional vegetation cover were derived from surface radiant temperature measurements and normalized difference vegetation index (NDVI). Application of the technique is made with reference to NS001 multispectral scanner measurements made by a C-130 aircraft over the Mahantango Watershed in Pennsylvania. The derived surface soil water content values were compared with those obtained from the Push Broom Microwave Radiometer (PBMR) aboard the same aircraft and with in-situ ground measurements. A large disparity was found to exist between all three measurements, suggesting that the surface becomes decoupled from the deeper substrate in regions of rapid drying, where large vertical gradients in soil water content may exist near the surface.

A new look at the simplified method for remote sensing of daily evapotranspiration

Abstract A modification of the so-called “Simplified Method” used to obtain the integrated daily evapotranspiration from surface radiant temperature over variable vegetation cover is proposed. Mathematically, the simplified equation takes the form Rn 24 − LE 24 =(T o13 − T a13 ) n , where Rn24 and LE24 are, respectively, the integrated net radiation and evapotranspiration over a 24-h period and T013 and Ta13 are, respectively, the surface radiant and the 50-m air temperatures at 1300 local time. B and n are pseudo constants given as functions of the normalized difference vegetation index (NDVI), expressed as a scaled index N*. Both N* and Ta13 are obtained with the aid of remotely determined measurements, which are viewed on scatterplots of T013 versus NDVI.

Probable causes of the abnormal ridge accompanying the 2013–2014 California drought: ENSO precursor and anthropogenic warming footprint

The 2013–2014 California drought was initiated by an anomalous high-amplitude ridge system. The anomalous ridge was investigated using reanalysis data and the Community Earth System Model (CESM). It was found that the ridge emerged from continual sources of Rossby wave energy in the western North Pacific starting in late summer and subsequently intensified into winter. The ridge generated a surge of wave energy downwind and deepened further the trough over the northeast U.S., forming a dipole. The dipole and associated circulation pattern is not linked directly with either El Nino–Southern Oscillation (ENSO) or Pacific Decadal Oscillation; instead, it is correlated with a type of ENSO precursor. The connection between the dipole and ENSO precursor has become stronger since the 1970s, and this is attributed to increased greenhouse gas loading as simulated by the CESM. Therefore, there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013–2014 and the associated drought.

Effects of urbanization on the aquatic fauna of the Line Creek watershed, Atlanta—a satellite perspective

Abstract Impervious surface area (ISA) was derived for a period from 1979 to 1997 from Landsat MSS and TM data for the Line Creek watershed that lies to the south of the city of Atlanta, GA. The change in ISA is presented as an ecological indicator to examine the cumulative water resource impacts on mussel population in three sub-watersheds of Line Creek—namely, Line, Flat, and Whitewater creeks. The satellite analysis shows that ISA expansion occurred substantially from 1987 to 1997 and is predominantly in industrial, commercial, and shopping center (ICS) complexes but also in smaller lot-size residential development. Evidence of mussel habitat degradation is indicated and loss of species (in the region of 50 to 70%) is present in areas where ISA expansion is observed—specifically in ICS complex development in and around Peachtree City that drains directly into the Line and Flat creeks. This is in marked contrast to Whitewater Creek where overall development of ISA is less and no major loss of mussel species is observed.

Increasing water cycle extremes in California and in relation to ENSO cycle under global warming

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)—in particular, extreme El Niño and La Niña events that modulate Californias climate not only through its warm and cold phases but also its precursor patterns.

Observational and Synoptic Analyses of the Winter Precipitation Regime Change over Utah

AbstractPrevious studies have indicated a widespread decline in snowpack over Utah accompanied by a decline in the snow–precipitation ratio while anecdotal evidence claims have been put forward that measured changes in Utah’s snowpack are spurious and do not reflect actual change. Using two distinct lines of investigation, this paper further analyzes the winter precipitation regime in the state of Utah. First, by means of observation-based, gridded daily temperature, precipitation, and remotely sensed data, as well as utilizing a climatological rain–snow threshold (RST) temperature method, the precipitation regime of Utah was scrutinized. Second, a comprehensive synoptic analysis was conducted as an alternate means that is independent from surface observations. It was found that the proportion of winter (January–March) precipitation falling as snow has decreased by 9% during the last half century, a combined result from a significant increase in rainfall and a minor decrease in snowfall. Meanwhile, observ...

Length Scale Analysis of Surface Energy Fluxes Derived from Remote Sensing

Abstract Wavelet multiresolution analysis was used to examine the variation in dominant length scales determined from remotely sensed airborne- and satellite-derived surface energy flux data. The wavelet cospectra are computed between surface radiometric temperature, fractional vegetation, and derived energy fluxes at airborne (12 m) and Advanced Very High Resolution Radiometer (AVHRR) (1000 m) resolutions. Length scale analysis of high-resolution data shows that small-scale variability in temperature dominates over other effects. Analysis of coarse-resolution data shows that small-scale variations in vegetation are important, although the large-scale variation in radiometric temperature dominates the derived fluxes. This is determined to be a result of the fact that, at smaller scales, the incoming solar radiation effect is muted by the small-scale variability in vegetation, temperature, and albedo, whereas at coarser scales, the large-scale effect of incoming radiation on temperature dominates over the ...