YaBeSH Digital Library http://localhost:80/yetl1 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2019-12-04T08:16:31Z Uncertainty of Reference Pixel Soil Moisture Averages Sampled at SMAP Core Validation Sites http://yetl.yabesh.ir/yetl1/handle/yetl/4263902 Uncertainty of Reference Pixel Soil Moisture Averages Sampled at SMAP Core Validation Sites Chen, Fan; Crow, Wade T.; Cosh, Michael H.; Colliander, Andreas; Asanuma, Jun; Berg, Aaron; Bosch, David D.; Caldwell, Todd G.; Collins, Chandra Holifield; Jensen, Karsten Høgh; Martínez-Fernández, Jose; McNairn, Heather; Starks, Patrick J.; Su, Zhongbo AbstractDespite extensive efforts to maximize ground coverage and improve upscaling functions within core validation sites (CVS) of the NASA Soil Moisture Active Passive (SMAP) mission, spatial averages of point-scale soil moisture observations often fail to accurately capture the true average of the reference pixels. Therefore, some level of pixel-scale sampling error from in situ observations must be considered during the validation of SMAP soil moisture retrievals. Here, uncertainties in the SMAP core site average soil moisture (CSASM) due to spatial sampling errors are examined and their impact on CSASM-based SMAP calibration and validation metrics is discussed. The estimated uncertainty (due to spatial sampling limitations) of mean CSASM over time is found to be large, translating into relatively large sampling uncertainty levels for SMAP retrieval bias when calculated against CSASM. As a result, CSASM-based SMAP bias estimates are statistically insignificant at nearly all SMAP CVS. In addition, observations from temporary networks suggest that these (already large) bias uncertainties may be underestimated due to undersampled spatial variability. The unbiased root-mean-square error (ubRMSE) of CSASM is estimated via two approaches: classical sampling theory and triple collocation, both of which suggest that CSASM ubRMSE is generally within the range of 0.01?0.02 m3 m?3. Although limitations in both methods likely lead to underestimation of ubRMSE, the results suggest that CSASM captures the temporal dynamics of the footprint-scale soil moisture relatively well and is thus a reliable reference for SMAP ubRMSE calculations. Therefore, spatial sampling errors are revealed to have very different impacts on efforts to estimate SMAP bias and ubRMSE metrics using CVS data. 2019-01-01T00:00:00Z Decisive Atmospheric Circulation Indices for July–August Precipitation in North China Based on Tree Models http://yetl.yabesh.ir/yetl1/handle/yetl/4263901 Decisive Atmospheric Circulation Indices for July–August Precipitation in North China Based on Tree Models Tong, Xuan; Yan, Zhongwei; Xia, Jiangjiang; Lou, Xiao AbstractNumerous circulation indices have been applied in practical climate services focused on regional precipitation. It is beneficial to identify the most influential or decisive indices, but this is difficult with conventional correlation analyses because of the underlying nonlinear mechanisms for precipitation. This paper demonstrates a set of the most influential indices for July?August precipitation in North China, based on the recursive random forest (RRF) method. These decisive circulation indices include the Polar?Eurasia teleconnection, North African subtropical high ridge position, India?Burma trough, Antarctic Oscillation, Northern Hemisphere polar vortex central latitude, North Atlantic Oscillation, and western Pacific subtropical high northern boundary position. Some of these factors have been recognized as directly influential to the regional precipitation, for example, those of the northwestern Pacific subtropical high; however, some are not easily understood. Decision tree (DT) models using these indices were developed to facilitate composite analyses to explain the RRF results. Taking one of the most interesting DT rules as an example, when the North African subtropical high ridge position is sufficiently far south, an anomalous anticyclone occurs in the upstream and an anomalous cyclone in the downstream of North China. This is unfavorable for northward moisture transport in eastern China and hence causes less precipitation in North China than climatology. The present results are not only helpful for improving diagnostic models of regional precipitation, but also enlightening for exploring how global climate change could impact a region by modulating large-scale circulation patterns. 2019-01-01T00:00:00Z A Multilayer Soil Moisture Dataset Based on the Gravimetric Method in China and Its Characteristics http://yetl.yabesh.ir/yetl1/handle/yetl/4263900 A Multilayer Soil Moisture Dataset Based on the Gravimetric Method in China and Its Characteristics Wang, Aihui; Shi, Xueli AbstractBased on the gravimetric-technique-measured soil relative wetness and the observed soil characteristic parameters from 1992 to 2013 in China, this study derives a user-convenient monthly volumetric soil moisture (SM) dataset from 732 stations for five soil layers (10, 20, 50, 70, and 100 cm). The temporal?spatial variations in SM and its relationship with precipitation (Pr) in different subregions are then explored. The magnitude of SM is relatively large in south China and is low in northwest China, and it generally increases with soil depth in each region. The maximum SM appears in spring and/or autumn and the minimum in summer, and the SM seasonality does not vary as distinctly as that of Pr. For the top three soil layers (10-, 20-, and 50-cm levels), the linear trend analysis indicates an overall increasing SM tendency, and the mean trends (averaged across stations with trends passing a 95% significance level test) are 9.35 ? 10?7, 7.37 ? 10?3, and 2.45 ? 10?3 cm3 cm?3 yr?1, respectively. SM memory depends on the soil depth and regions, and it has longer retention time in the deeper layers. Furthermore, the correlation between SM and antecedent Pr varies with soil depth and lag time. The antecedent Pr anomaly (1 or 2 months in advance) can be used to some extent as a surrogate SM anomaly in most regions except for in arid regions. This result is further demonstrated by the relationships between the SM anomaly and the standardized precipitation index. The current SM dataset can be used in various applications, such as validating satellite-retrieved products and model outputs. 2019-01-01T00:00:00Z The Role of Hydrological Initial Conditions on Atmospheric River Floods in the Russian River Basin http://yetl.yabesh.ir/yetl1/handle/yetl/4263899 The Role of Hydrological Initial Conditions on Atmospheric River Floods in the Russian River Basin Cao, Qian; Mehran, Ali; Ralph, F. Martin; Lettenmaier, Dennis P. AbstractA body of work over the last decade or so has demonstrated that most major floods along the U.S. West Coast are attributable to atmospheric rivers (ARs). Recent studies suggest that observed changes in extreme precipitation associated with a general warming of the western United States have not necessarily led to corresponding changes in floods, and changes in antecedent hydrological conditions could be a primary missing link. Here we examine the role of antecedent soil moisture (ASM) conditions on historical AR flooding on California?s Russian River basin, a coastal watershed whose winter precipitation extremes are dominated by ARs. We examined the effect of observed warming on ASM for the period 1950?2017. We first constructed an hourly precipitation product at 1/32° spatial resolution. We used the Distributed Hydrology Soil Vegetation Model (DHSVM) to estimate storm total runoff volumes and soil moisture. We found that up to 95% of peaks-over-threshold (POT) extreme discharge events were associated with ARs. The storm runoff?precipitation ratio generally increased with wetter prestorm conditions, and the relationship was stronger as drainage area increased. We found no trends in extreme precipitation but weak downward trends in extreme discharge. The latter were mostly consistent with weak downward trends in the first 2-day storm precipitation. We found no trends in ASM; however, ASM was significantly correlated with peak flow. The ASM was affected more by antecedent precipitation than evapotranspiration, and hence temperature increases had weak effects on ASM. 2019-01-01T00:00:00Z