Impact of climate change on rawa river water source in lake Lindu watershed, Central Sulawesi, Indonesia

. Global Climate change has been discussed in the High-Level Conference in Rio de Janeiro, Brazil in 1992 and has given more impacts in the world. One of the global climate exchanges is the rising of intensity and frequency of climate extreme which included drought, flood, and hurricane. The objective of this study was to investigate the effects of climate change on evapotranspiration and rainfall for river water discharge of Rawa. The investigation has been carried out using daily data and analyzed on a daily, monthly and yearly. The rain stations that represent the location of this research are Palolo, Kulawi, and Wuasa. Climatological station nearest to the research station used Bora. Climate trends and projected changes in the method of Makesens analysis (Mann-Kendall, Sens) and the correlation of rainfall and evapotranspiration discharge used linear regression equation. Similarly, the correlation between changes in soil water storage with rainfall, evapotranspiration, and discharge was analyzed in a linear manner. The conclusion of this study is the climate changes in the River of Rawa watershed was characterized by slowly increasing temperature, increasing rainfall, and decreasing discharge.


Introduction
Global Climate change has been discussed in the High-Level Conference in Rio de Janeiro, Brazil in 1992 and has given more impacts in the world. One of the global climate exchanges is the rising intensity and frequency of climate extreme which included drought, flood, and hurricane. Global climate change that occurs in addition to impacting on the increase or decrease of rain in an area, rising temperatures, can also be associated with changes in season patterns, wind patterns, air humidity, and solar irradiance. Increased rainfall as a watershed input due to global climate aberration will affect river flow discharge, both on an annual and seasonal basis. The purpose of this research is to know the impact of climate change on river water discharge related to climate factors such as temperature, air humidity, solar irradiance, wind speed, evapotranspiration, solar radiation, and rain. Climate components and climate change trends will be analyzed and further projected in the next few years.
The research was conducted in River of Rawa which is an outlet of Lake Lindu watershed, which is administratively located in Lindu Sub-district, Sigi Regency, Central Sulawesi Province, Indonesia. Geographically situated at 1 o 3'-1 o 58' South Latitude and 119 o 57'-120 o 22' East Longitude. Lake Lindu's watershed area is 546.056 km 2 . The location of the study is presented in Fig. 1.

Materials and methods
The data used in this research are primary data and secondary data. Primary data are field survey to know condition of Lake Lindu watershed, while secondary data are as follows: 1) monthly rainfall data Kulawi Station, Palolo and Wuasa (1993-2017), 2) climatology data of Bora Station (1993-2017), 3) daily Rawa River (2002-2014), 4) topographic map scale of 1:50,000. To determine the effect of climate change on Rawa River debit, it is necessary to 1) calculate region rainfall, 2) calculate evapotranspiration, 3) create discharge model, 4) calculate groundwater storage, and 5) detect climate change and its projection.

Region rainfall
Calculation of the rain of the region using the equation Polygon Thiessen [1][2][3][4]: Based on the topographic map and the location of the rain station, the influence for each rain station Kulawi Station (0.37), Palolo (0.30) and Wuasa (0.33) will be calculated.

Discharge model
The discharge model uses the equation [2,10] Data inputs are historical discharge, monthly rainfall, and evapotranspiration.

Soil water storage
The equations used [2,10] dS = R -ETo -Q' Data inputs are monthly rainfall, monthly evapotranspiration, dan monthly discharge.

Detect of climate change
Using the Mann-Kendall equation 1 0 Input data are temperature, relative humidity, wind velocity, time of sunshine, rainfall, evapotranspiration, soil water storage, and discharge, all of which are monthly data.

Climate and water balance changes
The time series curves of the Rawa River climate components are presented in Fig. 2, and the results of the calculation of climate change by the Mann-Kendall method are shown in Table 2.  From the calculation results with the Mann-Kendall method in Table 2 it can be seen that the temperature shows a change in climate with a significant upward trend except in October. Wind speeds are changing climate with significant downward trend except in March and October. Long sun radiation shows climate change with the downward trend but not significant except in January. Solar radiation shows climate change towards positive and negative but not significant except in January, June, August, and December. The average monthly rainfall indicates climate change is positive and negative but not significant except in July there is no climate change. Evapotranspiration shows climate change with significant downward trend except in February, March, September, November, and December. Average discharge indicates climate change is positive and negative but insignificant, except in December there is no trend. Soil water storage shows a significant climate change with a positive trend. Based on these climatic components it can be said that in the Lake Lindu watershed there is a significant climate change.

Estimated water discharge of Rawa River
This study aims to find whether or not there will be changes in river water discharge due to local climate change. For that, we need to know the relationship between river flow with rainfall and evapotranspiration.  7 rain and evapotranspiration data. The relationship between the discharge observation data (Q) and the discharge forecast (Q') is shown in Fig. 3.
From Fig. 3 left, it can be seen that the evapotranspiration is almost no change in time, rainfall fluctuates and tends to experience a rising trend, the river flow is relatively stable there is a significant change, while soil water storage fluctuates in tandem with the ups and downs of rain. This shows that although the rain fluctuates, evapotranspiration is relatively stable and soil water storage fluctuates, but the water flow is relatively unchanged, which means there are other factors as the cause. While the right three image shows the relationship between the observed discharge data Q and the predicted Q data whose R2 value is relatively small, indicating the correlation is not good. This may be caused by factors other than rain and evapotranspiration affecting the discharge.  (Q). The same thing also happens in Fig. 4 right, where the change of soil water storage (dS) is inversely proportional to the flow of water (Q), that is, the greater the discharge and evapotranspiration, the soil water storage change will be smaller. There is an interesting thing that happened from the Fig. 4 left that is the relationship between the discharge and rain, where the more rain, the smaller the discharge. This indicates that discharge can not only be affected by rain and evapotranspiration factors but also other influencing factors, such as land cover.

Conclusions
Based on monthly hydro climatology data from 1993 to 2017 period, then analyzed by Mann-Kendall method, it can be concluded that there have been significant changes in climate in Lake Lindu watershed by considering the Z value is bigger or smaller than zero. Also, the change can also be seen in the increase in temperature and rainfall and the decrease in river flow gradually. This indicates the occurrence of climate change that affects the river discharge and soil water storage changes.