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.

Iran is experiencing unprecedented climate-related problems such as drying of lakes and rivers, dust storms, record-breaking temperatures, droughts, and floods. Here, we use the ensemble of five high-resolution climate models to project maximum and minimum temperatures and rainfall distribution, calculate occurrences of extreme temperatures (temperatures above and below the historical 95th and 5th percentiles, respectively), analyze compound of precipitation and temperature extremes, and determine flooding frequencies across the country. We found that compared to the period of 1980–2004, in the period of 2025–2049, Iran is likely to experience more extended periods of extreme maximum temperatures in the southern part of the country, more extended periods of dry (for ≥120 days: precipitation <2 mm, Tmax ≥30 °C) as well as wet (for ≤3 days: total precipitation ≥110 mm) conditions, and higher frequency of floods. Overall, the combination of these results projects a climate of extended dry periods interrupted by intermittent heavy rainfalls, which is a recipe for increasing the chances of floods. Without thoughtful adaptability measures, some parts of the country may face limited habitability in the future.

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The future of extreme climate in Iran.

SWAT+ is a completely restructured version of the Soil and Water Assessment Tool (SWAT) that was developed to face present and future challenges in water resources modeling and management and to meet the needs of the worldwide user community. It is expected to improve code development and maintenance; support data availability, analysis, and visualization; and enhance the model's capabilities in terms of the spatial representation of elements and processes within watersheds. The most important change is the implementation of landscape units and flow and pollutant routing across the landscape. Also, SWAT+ offers more flexibility than SWAT in defining management schedules, routing constituents, and connecting managed flow systems to the natural stream network. To test the basic hydrologic function of SWAT+, it was applied to the Little River Experimental Watershed (Georgia) without enhanced overland routing and compared with previous models. SWAT+ gave similar results and inaccuracies as these models did for streamflow and water balance. Taking full advantage of the new capabilities of SWAT+ regarding watershed discretization and landscape and river interactions is expected to improve simulations in future studies. While many capabilities of SWAT have already been enhanced in SWAT+ and new capabilities have been added, the model will continue to evolve in response to advancements in scientific knowledge and the demands of the growing worldwide user community. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

Introduction to SWAT+, A Completely Restructured Version of the Soil and Water Assessment Tool†

Climate change and agriculture: Impacts and adaptive responses in Iran

The water resources of Tamor River Basin in the eastern Himalayas of Nepal is heavily tapped for agricultural water use and hydropower production. Several studies show that the hydrology of the Himalayan River Basins is vulnerable to climate change. Topographical variations, data scarcity and its complex climate have always been barriers to achieving realistic simulation of the hydrological regime in the Himalayan River Basins, and the Tamor River Basin is no different. In hydrological response unit (HRU) based models, fixing the number of HRUs and sub-basins has a tendency towards confusion. This is especially true in regions with altitudinal and climatic variations. Therefore, this study aims to evaluate the SWAT model performance uncertainty associated with the number of sub-basins, HRUs, and elevation bands and quantify the impact of climate change on streamflows in the Tamor River Basin. Future climate scenarios were developed for three different time frames, the 2030s, 2060s, and 2080s, based on an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) and four Regional Climate Models (RCMs) under the Representative Concentration Pathways (RCP4.5 and RCP8.5) scenarios. The linear scaling method (LSM) of bias correction was used to bias-correct the climate data and then fed into the SWAT model to simulate the future streamflows of the basin. An increase in the annual average maximum temperature (+4 °C) and minimum temperature (+5.5 °C), and a decrease in precipitation (−4.5%) is projected by the end of the twenty-first century under RCP8.5 scenarios. The study found that the future climate could decrease the streamflow by over 8.5% during the twenty-first century under RCP8.5 scenarios. The results show elevation bands (EBs) to be more significant compared to HRUs and sub-basins (SBs) in getting a robust hydrological model in the Himalayan region. The estimates prepared in this study would be beneficial for hydropower developers, planners and policymakers, and water resource managers in developing adaptation strategies to offset the negative impact of climate change in the Tamor River Basin.

Evaluation and application of a SWAT model to assess the climate change impact on the hydrology of the Himalayan River Basin

Water resources availability in the semiarid regions of Iran has experienced severe reduction because of increasing water use and lengthening of dry periods. To better manage this resource, we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semiarid region of Iran. Future climate scenarios for 2020–2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using the Soil and Water Assessment Tool to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. The Sequential Uncertainty Fitting Version 2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program called critical continuous day calculator was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB, freshwater availability will increase from 1716 to 2670 m3/capita/year despite an increase of 28% in the population in 2025 in the B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long-term average irrigated wheat yield, however, will increase in the south by 1.2%–21% in different subbasins; but for rain-fed wheat, this variation is from −4% to 38%. The results of critical continuous day calculator showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, whereas increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative whereas other areas will experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.

Analyses of the impact of climate change on water resources components, drought and wheat yield in semiarid regions: Karkheh River Basin in Iran

The paradigm of integrated water resources management requires coupled analysis of hydrology and water resources in a river basin. Population growth and uncertainties due to climate change make historic data not a reliable source of information for future planning of water resources, hence necessitating climate and landuse change impact studies. This work presents an integrated modeling approach by linking Soil and Water Assessment Tool (SWAT) and MODSIM. While SWAT produces hydrologic and water resources information, MODSIM provides a decision support system for water allocation. We used the coupled SWAT–MODSIM to analyze the effects of climate and cropping pattern changes on agricultural and hydroenergy production in the Karkheh River Basin, a semiarid region in south-west of Iran. Cropping patterns were considered by limiting the cereal production to 50 % (S1, near to historic), 17 % (S2), and 83 % (S3) of total agricultural areas. The future climate was provided by the Canadian Global Coupled Model (CGCM 3.1 version T63) for A1B, A2, and B1 scenarios. The results showed that based on future climate changes and landuse scenarios, wheat production had a large variation in five economically important agricultural regions ranging from 33,000 ton year−1 (S2-A1B) to 74,000 ton year−1 (S3-A2). Similarly, energy production, while increasing from 614 to 1,100 GWH in A2, decreased from 614 to 464 GWH in B1 climate scenario. Our analyses indicate that cropping pattern change can be used as an effective tool to adapt to the negative impacts of climate change.

https://ssl.tamu.edu/media/91252/vaghefi-integration-of-hydrologic.pdf

Integration of hydrologic and water allocation models in basin-scale water resources management considering crop pattern and climate change: Karkheh River Basin in Iran

S. J. Mousavi

Papers

Analyses of the impact of climate change on water resources components, drought and wheat yield in semiarid regions: Karkheh River Basin in Iran

Integration of hydrologic and water allocation models in basin-scale water resources management considering crop pattern and climate change: Karkheh River Basin in Iran

An Imperialist Competitive Algorithm Artificial Neural Network Method to Predict Runoff