Statistics for Spatial Data.

Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near-complete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

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Global observed changes in daily climate extremes of temperature and precipitation

A review of drought concepts

More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.

http://science.sciencemag.org/content/sci/328/5984/1382.full.pdf

Climate change will affect the Asian water towers.

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

A fully Bayesian approach to parameter estimation and inference in conceptual rainfall-runoff models (CRRMs) is presented. Computations are performed using a Markov chain Monte Carlo (MCMC) method based on the Metropolis-Hastings algorithm. Single-site and block updating schemes are used for model parameters subject to nonnegativity restrictions as well as interval, equality, and order constraints. Diagnostics for the convergence of the Markov chain and CRRM assessment are also considered. The MCMC approach produces samples from the joint posterior distribution of the model parameters. This provides more information than single-point estimates and avoids the need to use a normal approximation to the posterior as the basis for inference. The methodology is demonstrated using an eight-parameter conceptual rainfall-runoff model and two case studies from southeastern Australia. The first case study considers a watershed with high runoff yield over a 12-year period. The second case study considers a watershed with low yield over a 17-year period. The results indicate that (1) Bayesian methods provide an objective framework for model criticism and choice, (2) the proposed strategies for handling constraints on model parameters are effective, (3) the model parameters are sensitive to likelihood function selection, (4) the conventional approach of using a power transformation and an autoregressive process to stabilize error variance and model dependence in the residuals may have limited success, and (5) some care is required in the implementation of the MCMC approach and reliable results will be difficult to obtain when CRRM complexity exceeds the limitations of the rainfall-runoff data at hand. A key finding is that the MCMC scheme presented herein provides a powerful means of identifying specific inadequacies in the structure of CRRMs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900363

A Markov Chain Monte Carlo Scheme for parameter estimation and inference in conceptual rainfall‐runoff modeling

The Technical Paper addresses the issue of freshwater. Sea level rise is dealt with only insofar as it can lead to impacts on freshwater in coastal areas and beyond. Climate, freshwater, biophysical and socio-economic systems are interconnected in complex ways. Hence, a change in any one of these can induce a change in any other. Freshwater-related issues are critical in determining key regional and sectoral vulnerabilities. Therefore, the relationship between climate change and freshwater resources is of primary concern to human society and also has implications for all living species.

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Climate Change and Water: Technical Paper VI

Low-yielding catchments with ephemeral streams involve highly nonlinear relationships between rainfall and runoff, and there is much less documentation and appreciation of the ability to predict streamflow in these veiy difficult cases than in humid catchments. The predictions of three conceptual rainfall-runoff models are assessed in three low-yielding, emphemeral streams over a 10-year period. The models are a simple conceptual model, Generalized Surface inFiltration Baseflow (GSFB; eight parameters), a hybrid metric/conceptual model, Identification of Hydrographs and Components from Rainfall, Evaporation and Streamflow data (IHACRES; six parameters), and a complex conceptual model, the Large Scale Catchment Model (LASCAM; 22 parameters). The Salmon (0.82 km2), Stones (15 km2), and Canning (517 km2) catchments in Western Australia were selected for their range of sizes and low runoff yields (1.6–12.2% of rainfall). Their behavior is representative of a large part of Australia and semiarid regions, where antecedent conditions are critical determinants of streamflow response to rainfall. Such catchments provide a stern test of the capability of conceptual models. Five-year calibration and validation performances were assessed with a range of statistics. The models were run daily but performance was assessed on both a daily and monthly basis by aggregating daily model streamflows and observations up to monthly. The models performed well, particularly in the monthly case where often more than 90% of the variance of observed streamflow was explained in simulation on independent periods. However, while the simple conceptual model is adequate for monthly time periods, the daily simulation results indicate that a slightly more complex model (the hybrid model or the complex conceptual model) is required for daily predictions in these dry catchments. The model simulation results extend the following notion of Jakeman and Hornberger [1993] from humid to semiarid ephemeral catchments: that a model of about six parameters, albeit in an appropriate model structure, is sufficient to characterize the information in rainfall-discharge time series over a wide range of catchment sizes. Models of such modest complexity also predict runoff with good accuracy outside calibration periods, even in ephemeral, low-yielding catchments. The simulation results highlight the critical importance of the deep groundwater and antecedent moisture conditions on stream yields in ephemeral catchments and point to the desirability of accounting for these factors in arid-zone modeling.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96WR02840

Performance of conceptual rainfall‐runoff models in low‐yielding ephemeral catchments

Since the mid-1970s the climatic changes that have taken place in southwest Western Australia have generated a variety of impacts, the most prominent of which is a reduction in dam inflows of at least 50 percent. These impacts were the catalyst for the formation of the Indian Ocean Climate Initiative in 1998, a research partnership between two national research organizations and several state government departments and agencies. This paper describes the key scientific findings of the Initiative with respect to the nature of the climatic changes that have taken place within the region, explores the factors that might have caused these changes, and describes the most recent climate projections for the region. We reflect on the factors leading to the rapid acceptance of the research outcomes from the Initiative, the impact of the Initiative on policy development across Australia and its likely evolution post-2006.

Bryson C. Bates

Papers

Climate change and water.

A Markov Chain Monte Carlo Scheme for parameter estimation and inference in conceptual rainfall‐runoff modeling

Climate Change and Water: Technical Paper VI

Performance of conceptual rainfall‐runoff models in low‐yielding ephemeral catchments

Key findings from the Indian Ocean Climate Initiative and their impact on policy development in Australia