ارزیابی سامانه‌های گردآوری و نگاه‌داری آب باران برای تأمین آب اطفای حریق در جنگل‌ها و مراتع زاگرس (مطالعه موردی: جنوب‌غرب شیراز)

Introduction
Wildfires are among the most serious natural hazards threatening forest and rangeland ecosystems. Besides destroying vegetation, they reduce biodiversity, accelerate soil erosion, disrupt ecosystem services, and increase greenhouse gas emissions. In recent decades, rising temperatures, prolonged droughts, and changing precipitation patterns have increased both the frequency and severity of wildfires, particularly in the Zagros forests and rangelands of Iran. Rapid access to water during the initial stage of firefighting is one of the most critical factors determining the success of wildfire suppression. However, most mountainous areas of the Zagros region suffer from a scarcity of permanent water resources, long distances to available water sources, limited accessibility, and the difficulty of transporting water to fire sites. Meanwhile, rainwater harvesting (RWH), a well-established technology for arid and semi-arid regions, has mainly been used for domestic water supply, agriculture, livestock watering, runoff management, and vegetation restoration. Its application as an emergency water source for wildfire suppression has received relatively little attention. Therefore, this study aimed to evaluate the feasibility of using rainwater harvesting systems to supply part of the water required for wildfire suppression, identify the most suitable harvesting system, and propose general criteria for the design and site selection of such systems in the rugged forests and rangelands of the Zagros Mountains.
Materials and Methods
This applied research adopted a descriptive–analytical approach and was conducted in an approximately 868-ha forest and rangeland area located in the western and southwestern parts of Shiraz within the Zagros region. The study area is characterized by rugged mountainous terrain, an average elevation of about 2,100 m, a mean annual precipitation of approximately 312 mm, and an average annual evaporation of nearly 2,450 mm.
The required data were collected through a review of scientific literature, topographic, geological, land-use, and climatic information, digital elevation models, field surveys, and interviews with experts and local stakeholders. Existing water resources were first assessed, after which the water demand for the initial wildfire suppression operation was estimated using a design scenario based on firefighting discharge, operation duration, protected area, and conveyance losses. Various rainwater harvesting systems were then evaluated and compared with respect to runoff generation potential, storage capacity, topographic suitability, construction feasibility, implementation cost, use of locally available materials, accessibility for firefighting crews, environmental impacts, and multipurpose functionality in order to identify the most suitable alternative for the study area.
Results and Discussion
The results showed that approximately 125 m³ of water is required for the initial suppression of a wildfire affecting 50 ha, and this value was adopted as the design storage volume. Climatic analysis indicated that more than half of the annual precipitation occurs during winter and that most rainfall events precede the wildfire season. Consequently, favorable conditions exist for harvesting and storing rainwater for use during the dry period when wildfire risk is greatest. Field investigations further revealed that no permanent water source exists within the study area, while the nearest available water source is located approximately 10 km away. Combined with rugged terrain and limited road access, these conditions significantly hinder rapid firefighting operations.
Among the evaluated alternatives, a smoothed catchment surface combined with a storage cistern proved to be the most suitable system under the climatic and topographic conditions of the study area because it efficiently generates runoff, stores water throughout the dry season, and provides rapid access during emergency situations. To supply the required storage volume, the catchment area was estimated at 744 m² for a concrete catchment surface and 1,116 m² for a compacted earthen catchment surface. Owing to its higher runoff coefficient, the concrete surface reduced the required catchment area by approximately 33% compared with the earthen alternative. Nevertheless, the compacted earthen surface remains a practical option for economically constrained areas because of its lower construction cost and the possibility of using locally available materials. The results also indicate that selecting an appropriate rainwater harvesting system should consider not only technical performance but also economic conditions, construction capability, community participation, and local environmental characteristics.
Comparison with previous national and international studies demonstrated good agreement with earlier findings on rainwater harvesting and wildfire risk management. In addition to reducing dependence on surface and groundwater resources, decentralized rainwater harvesting systems can improve water availability during the critical initial phase of wildfire suppression and contribute to sustainable natural resource management and greater ecosystem resilience to drought and wildfire.
Conclusion
The findings indicate that the scarcity of local water resources, the long distance to existing water supplies, and difficult access in mountainous terrain are major constraints limiting effective initial wildfire suppression in the Zagros forests and rangelands. Conversely, the concentration of rainfall during the cold season provides suitable conditions for harvesting and storing rainwater for use during periods of high wildfire risk. Based on the technical and economic evaluation, a smoothed catchment surface coupled with a storage cistern was identified as the most appropriate rainwater harvesting system because of its simple construction, compatibility with local climatic and topographic conditions, adequate storage capacity, and rapid water availability during emergency operations. Nevertheless, the choice between concrete and compacted earthen catchment surfaces should be based on site-specific conditions, available financial resources, and construction capability. Overall, integrating rainwater harvesting systems into wildfire risk management programs can reduce response time, decrease environmental and economic losses, and improve the resilience of forest and rangeland ecosystems. Future studies should focus on optimizing the location of these systems using GIS,