Comparison of Land Use and Climate Change impacts on Runoff in a small mountainous catchment (Case Study: Garin dam catchment)

  Our Earth’s surface is warming rapidly and we can see social, economic and environmental impacts in the world. Failing to take sufficient action today entails potentially huge risks to our environment, economy, society and way of life into the future. This is the critical decade for action. Climate change and global warming will have direct and indirect impacts on water resources by accelerating the hydrological cycle and runoff. Hydrological simulation is an important approach to studying climate change impacts. With decreasing snowfall under climate change conditions, modeling of land use change in mountainous regions is an inherently difficult task Prediction of future changes in land use and climate change and its probability impacts on hydrological processes of watershed can be helpful for challenges of water resource manager and planners in the coming period that it is an important step in the correct planning and integrated management of watersheds. In this study, it has been coupled climate change scenarios, and land use change models with runoff models.
Data and In the present research,Future land use scenarios were modeled by initially calculating the rate of current land use changes between three times snapshots (1986, 2000 and 2014) on Garin dam watershed using Land Sat satellite images, and based on transition probabilities markov-chain and CA markov-chain were used to generate future land use changes for 2042. Markov chain models are essentially projection models that describe the probabilistic movements an individual in a system comprised of discrete states. When applied to land use and many other applications, Markov chains often specify both time and a finite set of states as discrete values. Transitions between the states of the system are recorded in the form of a transition matrix that records the probability of moving
from one state to another. The definition of a system as a finite Markov Chain requires a certain set of properties to hold (Stokey and Zeckhauser, 1978).
SDSM Model used for down scaling of rain and temperature data and Hadcm3 output used for prediction of Garin future climate. Also, in order to study land use change and climate change impacts on runoff SWAT model was used. The simulation coefficients for calibration and validation (table1 and 2) was reasonable and well thus, performance of the model is acceptable. The results show that the forest area will be increased and rangeland will be decreased until 2042 (table3). The Result of Markov -chain and CA Markov-Chain analysis indicate that landuse change will decrease run off rate under A2 and B2 scenarios in 2042. The results reveal that climate change impacts on reducing of runoff is more than land use change during 2042 to 2050 compared 2000 to 2010. Table1. the coefficients for Calibration for discharge simulation
br2 MSE P_factor R-factor R2 NS
0.36 0.39 0.47 0.03 0.60 0.59
Table2. the coefficients for Validation for discharge simulation
bR2 MSE P_factor R-factor R2 NS
0.51 0.16 0.39 0.04 0.67 0.66
Table3. Comparison of the landuses area in 2014(at the present time) and 2042(in the future) Year Natural
Forest Cultivated
Forest Rangeland Rockland
2014 2.35 0.82 14.63 3.24
2042 2.59 1.05 14.19 3.20   The NC,〖 br〗^2, R^2, MSE, P-factor and R-factor coefficients show that validation was better than calibration and both them reveals that performance of the model is reasonable and well. The results show that if trend be stable duration 1986 to 2014, the forest area will be increased by 2.28 percent and rangeland will be decreased by 2.07 percent until 2042 and also, mean precipitation will be reduced but mean temperature will has increased. The results indicate that rangland and rockland area decraesing and forest area increasing area cause to reduce runoff under A2 and B2 scenarios in the future time. Finally, the results show that influence of climate change on runoff reducing is more than effect of land use change from 2014 to 2042. The results can be used to improve management of Garin watershed and to focus on landuses damages and changes. The watershed studied has witnessed landuse change less than climate change effects on runoff rate. Without strong and rapid action there is a significant risk that climate change will undermine our society’s prosperity, health, stability and way of life. To minimize this risk, we must decarbonizes our economy and move to clean energy sources by 2050. That means carbon emissions must peak within the next few years and then strongly decline.