Abstract:A nonlinear function approach for the normalized complementary relationship evaporation model that is different from the methodology maintaining the symmetric complementary relationship with appropriate definitions of potential and wetenvironment evaporation is proposed and verified. This approach employs the definitions used in the advection-aridity model, wherein the potential is estimated using the Penman equation. Normalized by Penman potential evaporation, the complementary relationship model is expressed as a function describing the relationship between the evaporation ratio (the ratio of the actual to the Penman potential evaporation) and the proportion of the radiation term in Penman potential evaporation. The new nonlinear function proposed in the current study is approximately equivalent to the advection-aridity and the modified Granger models under conditions that are neither too wet nor too dry, but is more reasonable under arid and wet conditions. The new nonlinear function model performs well in estimating actual evaporation, as verified by the observed data from four sites under different land covers.

Abstract:A complementary relationship evaporation model has been proposed and verified based on evaluations of the advection-aridity model and the Granger's complementary relationship model (Granger model) in dimensionless forms. Normalized by Penman potential evaporation, the Granger model and the advection-aridity model have been transformed into similar dimensionless forms. Evaporation ratio (ratio of actual evaporation to Penman potential evaporation) has been expressed as a function of dimensionless variable based on radiation and atmospheric conditions. Similar dimensionless variables for the different functions have been used in the two models. By referring to the dimensionless variable from the advection-aridity model and the function from the Granger model, a new model to estimate actual evaporation was proposed. The performance of the new model has been validated by the observed data from four sites under different land covers. The new model is an enhanced Granger model with better evaporation prediction over the aforementioned different land covers. It also offers more stable optimized parameters in a grassland site than the Granger model. The new model somewhat approximates the advection-aridity model under neither too wet nor too dry conditions, but without its system bias.

Daily rainfall data from 485 stations in China over the period are used to examine changes in seasonal extreme rainfall. We focus on the temporal changes in their distribution, together with examination of the dependence of seasonal extreme rainfall on elevation. The validity of the stationarity assumption is investigated by testing for nonstationarities in the form of abrupt and slowly varying changes. The nonparametric Pettitt test is used to detect change points in the mean and variance of the rainfall distribution, while the presence of monotonic trends and trend magnitude is tested using Mann-Kendall test and Sen's slope estimator. Violation of the stationarity assumption is mostly associated with abrupt rather than gradual changes, and monotonic trends are generally not statistically significant. Most of the change points occurred in the 1980s, when China underwent a socioeconomic development. Extreme rainfall in autumn (spring and winter) points to a decreasing (increasing) tendency over the majority of the country, while summer extreme rainfall exhibits a 'dipole-like' structure, with an overall tendency towards increasing trends in the south and decreasing in the north. The parameters of the Generalized Extreme Value (GEV) distribution are used to examine the dependence of extreme rainfall on elevation. The location and scale parameters are negatively correlated with elevation, while orography does not appear to be an important control on the shape parameter. The dependence of GEV parameters on elevation is more pronounced in northern rather than southern China. We also investigated the relation between summer extreme rainfall and climate variability, focusing on the East Asia Summer Monsoon (EASM) index. EASM is negatively (positively) correlated with summer extreme rainfall over South (North) China. Considering the weakening trend of EASM in recent years, there is a potential water shortage in the North China Plain and increasing flood risk in the south.

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Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3.

Abstract. Water availability is one of the most important environmental controls on vegetation phenology, especially in semi-arid regions. It is often represented in terms of soil moisture in small-scale studies, whereas it tends to be represented by precipitation in large-scale (e.g., regional) studies. Clearly, soil moisture is the more appropriate indicator for root water uptake and vegetation growth/phenology. Its potential advantage and applicability needs to be demonstrated at regional scales. The paper presents a data-based regional study of the effectiveness of novel water and temperature-based indices to predict spring vegetation greenup dates based on the Normalized Difference Vegetation Index (NDVI) observations in the grasslands of Inner Mongolia, China. The macro-scale hydrological model, VIC (Variable Infiltration Capacity), is employed to generate a soil moisture database across the region. In addition to a standard index based on temperature, two potential hydrologybased indices for prediction of spring onset dates are defined, based on the simulated soil moisture data as well as on observed precipitation data. Results indicate that the correspondence between the NDVI-derived green-up onset date and the soil-moisture-derived potential onset date exhibits a significantly better correlation as a function of increasing aridity compared to that based on precipitation. In this way the soil-moisture-based index is demonstrated to be superior to the precipitation-based index in terms of capturing grassland spring phenology. The results also showed that both of the hydrological (water-based) indices were superior to the thermal (temperature-based) index in determining the patterns of grass green-up in the Inner Mongolia region, indicating water availability to be the dominant control on average. The understanding about the relative controls on grassland phenology and the effectiveness of alternative indices to capture these controls are important for future studies of vegetation phenology change under climate change.

Articles you may be interested inPhysical properties of epitaxial ZrN/MgO(001) layers grown by reactive magnetron sputtering J. Vac. Sci. Technol. A 31, 061516 (2013); 10.1116/1.4825349 Thermoelectric properties of epitaxial ScN films deposited by reactive magnetron sputtering onto MgO(001) substrates Structural and electrical characteristics of W-N thin films prepared by reactive rf sputtering J. Vac. Sci. Technol. A 21, 616 (2003); 10.1116/1.1564029Epitaxial growth of metastable δ-TaN layers on MgO(001) using low-energy, high-flux ion irradiation during ultrahigh vacuum reactive magnetron sputtering Epitaxial Ti 1Ϫx W x N alloys with 0рxр0.6 were grown on MgO͑001͒ substrates at 500°C by ultrahigh vacuum reactive magnetron sputtering from Ti and W targets in pure N 2 . X-ray diffraction, transmission electron microscopy ͑TEM͒, and cross-sectional TEM show that the 0.3-m-thick Ti 1Ϫx W x N(001) alloys are single crystals with the B1-NaCl structure. Rutherford backscattering spectroscopy investigations indicate that alloys with xу0.05 are slightly overstoichiometric with N/(TiϩW)ϭ1.06Ϯ0.05. The alloy lattice parameter a Ќ along the film growth direction is 4.251 Å, irrespective of the WN concentration, for xр0.41 and decreases slightly at higher concentrations. TEM analyses show that Ti 0.5 W 0.5 N(001) alloys have long-range CuPt-type atomic ordering on the cation sublattice. The room-temperature resistivity increases linearly from 13 ⍀ cm for TiN to 287 ⍀ cm for Ti 0.42 W 0.58 N due primarily to alloy scattering while the temperature coefficient of resistivity is positive in Ti 1-x W x N alloys with xр0.21 and negative for xϾ0.21 due to weak charge carrier localization. The superconducting critical temperature T c of Ti 1-x W x N alloys initially increases with x, due to a larger density of states at the Fermi level, consistent with valence band x-ray photoelectron spectroscopy measurements. T c reaches a maximum of 6.67 K at xϭ0.21 and decreases for larger x values.