Derivation of new design rainfall in Qatar using L-moment based index frequency approach

AbstractFor stormwater system design, flood estimation and many other environmental assessment tasks, design rainfall is an essential input. Estimation of design rainfall is generally made using a regionalization technique based on a regional database of observed rainfalls. Many countries have derived their own generalized design rainfall data, which are generally expressed in the form of intensity–duration–frequency (IDF) curves. In Qatar, situated in an arid region, the existing IDF data were developed in 1991 using a limited data set. This paper presents the development of new IDF data for the State of Qatar using the method of L-moments and the index regional frequency analysis approach. The daily rainfall data from 32 stations located in Qatar and nearby Gulf countries have been used to form a homogeneous region. It has been found that the Pearson Type 3 distribution best fits the 24-h duration annual maximum rainfall data in the Qatar region. For the ungauged case, a prediction equation is developed where mean annual maximum rainfall is expressed as a function of climatic and physiographic characteristics. From a leave-one-out validation, it has been found that the developed prediction equation can estimate mean annual maximum rainfall with a median relative error of about 5.5%. Finally, an approximate method is used to obtain design rainfalls for other durations due to the limitations of continuous pluviograph data in Qatar. The new set of IDF curves is based on a much bigger dataset than the existing 1991 IDF curves. It is expected that the new IDF curves will have wider application in Qatar and will provide a statistically sound basis for storm water design, flood and environmental studies. The method can be applied to other middle-eastern states and similar arid countries in the world

Estimation of design rainfall in arid region : a case study for Qatar using L moments

Design rainfall is a fundamental input to the planning, design and operation of many water and environmental projects. Most countries have derived their own generalised design rainfall data, which is generally expressed in the form of intensity-duration-frequency (IDF) curves. In Qatar, situated in arid region, the existing IDF data was developed in 1991 using a limited data set. This paper presents the development of new IDF data for the State of Qatar using method of L-moments and index regional frequency analysis approach with the mean rainfall as the scaling factor. The daily rainfall data from 32 stations located in Qatar and nearby Gulf countries has been used to form a homogeneous region based on the criteria of Hosking and Wallis. It has been found that the Pearson Type 3 distribution best fits the 24-hour duration annual maximum rainfall data in the Qatar region. For ungauged case, a prediction equation is developed where mean annual maximum rainfall is expressed as a function of physiographic characteristics. From a leave-one-out validation, it has been found the developed prediction equation can estimate mean annual maximum rainfall with a median relative error of 5.5%. Finally, an approximate method is used to obtain design rainfalls for other durations due to the limitations of continuous pluviograph data. The new set of IDF curves are based on a much bigger dataset than the existing 1991 IDF curves. It is expected that the new IDF curves will have wider application in Qatar and will provide a statistically sound basis for storm water design, flood and environmental studies

An exploratory study on the impact of climate change on design rainfalls in the state of Qatar

Intergovernmental Panel for Climate Change (IPCC) in its fourth Assessment Report AR4 predicts a more extreme climate towards the end of the century, which is likely to impact the design of engineering infrastructure projects with a long design life. A recent study in 2013 developed new design rainfall for Qatar, which provides an improved design basis of drainage infrastructure for the State of Qatar under the current climate. The current design standards in Qatar do not consider increased rainfall intensity caused by climate change. The focus of this paper is to update recently developed design rainfalls in Qatar under the changing climatic conditions based on IPCC's AR4 allowing a later revision to the proposed design standards, relevant for projects with a longer design life. The future climate has been investigated based on the climate models released by IPCC’s AR4 and A2 story line of emission scenarios (SRES) using a stationary approach. Annual maximum series (AMS) of predicted 24 hours rainfall data for both wet (NCAR-CCSM) scenario and dry (CSIRO-MK3.5) scenario for the Qatari grid points in the climate models have been extracted for three periods, current climate 2010-2039, medium term climate (2040-2069) and end of century climate (2070-2099). A homogeneous region of the Qatari grid points has been formed and L-Moments based regional frequency approach is adopted to derive design rainfalls. The results indicate no significant changes in the design rainfall on the short term 2040-2069, but significant changes are expected towards the end of the century (2070-2099). New design rainfalls have been developed taking into account climate change for 2070-2099 scenario and by averaging results from the two scenarios. IPCC’s AR4 predicts that the rainfall intensity for a 5-year return period rain with duration of 1 to 2 hours will increase by 11% in 2070-2099 compared to current climate. Similarly, the rainfall intensity for more extreme rainfall, with a return period of 100 years and duration of 1 to 2 hours will increase by 71% in 2070-2099 compared to current climate. Infrastructure with a design life exceeding 60 years should add safety factors taking the predicted effects from climate change into due consideration

Design rainfall in Qatar : sensitivity to climate change scenarios

Design rainfall is needed in the design of numerous engineering infrastructures such as urban drainage systems, bridges, railways, metro systems, highways and flood levees. Design rainfall is derived using regional frequency analysis approach based on observed rainfall data from a large number of stations within a homogeneous region. This paper provides an assessment of the possible impacts of climate change on design rainfalls in Qatar. The future climate conditions are established based on AR4 and A2 categories of emission scenarios (SRES) specified by the Intergovernmental Panel on Climate Change. Predicted 24-h annual maximum rainfall series for both the wet (NCAR-CCSM) and dry scenarios (CSIRO-MK3.5) for the Qatari grid points are extracted for three different periods, which are current (2000–2029), medium-term (2040–2069) and end-of-century climates (2080–2099). Using an L-moments-based index frequency approach, homogeneous regions are established and the best-fit distribution is then used to derive rainfall quantiles for average recurrence intervals (ARIs) of 2, 5, 10, 25, 50 and 100 years. The results show that there is no significant change in the design rainfalls in Qatar in the short term covering 2040–2069; however, a significant change is predicted at the end of century covering 2080–2099. Updated design rainfalls are estimated considering climate change scenarios for the period of 2080–2099 by averaging results from the wet and dry climate scenarios. The increase in 24-h annual maximum rainfall for the period 2080–2099 (compared with the current period 2000–2029) is found to be in the range of 68 and 76 % for 100-year ARI. For the typical design ARIs of 10–20 years, the increase in design rainfall is found to be in the range of 43 and 54 %. The method presented in this study can be applied to other arid regions, in particular to the Middle Eastern countries

First flush analysis using a rainfall simulator on a micro catchment in an arid climate

Urban runoff water from simulated rainfall for three different land uses (residential, industrial, commercial) at six different locations of Doha, Qatar was analysed for physico-chemical parameters such as, trace metals, pH, total suspended solids (TSS), total organic carbon (TOC), total phosphorus (TP), total kjeldahl nitrogen (TKN) and polyaromatic hydrocarbons (PAHs). Rainfall events with two different intensities (40 mm/h and 20 mm/h) were simulated in a micro catchment area (4.55 × 4.55 m2) using a specially designed portable rainfall simulator. Out of six sites, runoff samples were collected from five sites with paved surfaces. The study results demonstrated significant concentration of TSS, Cu, Fe, Mn and Zn in the urban runoff exceeding the Qatar Ministry of Municipality and Environment (MME) and Tropical Australian Standards. The first flush effect was also investigated during the experiment which exhibited first flush effect of selected pollutants (TSS, TKN, TP, TOC and heavy metals) at five study sites with impervious surfaces. The magnitude of the first flush varies across the study sites and was found to be affected by the surface texture of the sites. Analysis of variance revealed that, rainfall intensity has limited effect on the first flush in the studied scenarios, however, first flush effects showed relation with the event mean runoff concentration. Furthermore, strong positive correlations were observed between analysed water quality parameters, particularly between TSS, TOC and metals. This study is the first study investigating first flush in Qatar's capital, Doha which will provide a ground for future researcher to design appropriate stormwater treatment devices that will capture and treat the first flush for significant reduction of urban stormwater pollution