The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an...

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A Multiscalar Drought Index Sensitive to Global Warming: The Standardized Precipitation Evapotranspiration Index

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

A review of drought concepts

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

The topography of a catchment has a major impact on the hydrological, geomorphological. and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered.

Digital terrain modelling: A review of hydrological, geomorphological, and biological applications

Bayesian methods are used to discriminate among alternative structures of the covariance matrix of the disturbances of hydrologic regression schemes; moreover, the covariance matrix is allowed to be non-scalar. Different alternative functional forms, which the hydrologic regression may also have, are also discriminated through the proposed methodology.

Choosing among hydrologic regression models: 2. Extensions to the standard model

The aggregated‐precipitation input to a catchment is defined in this work as one that minimizes an objective measure of the difference between the calculated and the observed hydrograph. This measure is different from the evaluated mean areal precipitation using, for example, Thiessen polygons. Once the aggregated inputs are derived for a set of storm events over a given basin, the relationships between the mean areal precipitation, the precipitation at a point inside the basin, and the derived aggregated input may be analyzed to detect linkages among them. We represented this linkage by a weighting function, which multiplies single raingage records to obtain the aggregated input. Streamflow measurements and a simple model of the rainfall‐runoff process are used to evaluate this weighting function, which varies during the storm. The ultimate goal of this work is to use this relationship to evaluate the aggregated input for ungaged storm events. In this preliminary phase, only linearly distributed and aggr...

Representation of Spatial Variability of Rainfall in Aggregated Rainfall-Runoff Models

Climate variability and change in precipitation and streamflows of several Patagonian basins are analysed using both parametric and non-parametric tests and simulation models. Additional hydroclimatic (e.g. soil moisture, evapotranspiration, etc.) time series, obtained using a parametric monthly water balance model, were also analysed. The climate change characteristics are defined using results from several GCMs using a climate scenario generator (MAGICC/ SCENGEN software). All GCM model results for the region show increases in temperature but are more variable in their estimates of precipitation. Synthetic traces of hydroclimatic variables, based on the GCM results, were then generated as inputs to the rainfall-runoff model. A non-parametric technique was used to evaluate the feasibility of early detection of climate change impact in the traces. The impact of climatic precursors such as ENSO (El Nino/ Southern Oscillation) in the hydro-climatology of the Patagonian basins is also analysed in this work.

Climate variability and climate change in Patagonian rivers

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Sustainable planning, management, and evaluation of water resources in irrigation District No. 041, Río Yaqui, Mexico.

We present a detailed overview of the Multi-model Multi-product Streamflow Forecasting (MMSF) Platform, which has been developed recently at the University of Arizona under the NASA SERVIR Program,...

Juan B. Valdés

Papers

Choosing among hydrologic regression models: 2. Extensions to the standard model

Representation of Spatial Variability of Rainfall in Aggregated Rainfall-Runoff Models

Climate variability and climate change in Patagonian rivers

Sustainable planning, management, and evaluation of water resources in irrigation District No. 041, Río Yaqui, Mexico.

Detailed Overview of the Multimodel Multiproduct Streamflow Forecasting Platform