An assessment of Jangkok River's water system conditions is needed to its monitoring watershed criticality to prevent various problems and for conservation purposes. The aim of this research was to assess the condition of Jangkok River's water system over the past 17 years using the Republic of Indonesia Minister of Forestry Regulation No. 61/Menhut-II/2014 concerning Monitoring and Evaluation of Watershed Management. The assessment results showed that Jangkok is in a good conditions but it tends to deteriorate that was indicated by the tends of increasing Flow Regime Coefficient and Annual Flow Coefficient. The mean of Flow Regime Coefficient's value of upstream is 65.66 (medium) and downstream is 333.63 (very high), while the increasing rate of 7.72 and 59.13 a year respectively. The mean Annual Flow Coefficient is 0.14 for upstream and downstream 0.22, which increases 0.99% and 0.93% a year respectively. The tendency of the value of the Water Use Index decreased with an annual average of 0.31 and a rate of decline of 0.005 a year. The assessment result shows that Jangkok is GOOD in water system condition but it requires more attention to maintain its function and ensure water sustainability.

Determination of irrigation channel dimensions is determined by the number of consumptive use values that are empirically determined by the potential evapotranspiration value (ETo). Due to the limited lysimeter measurement data, the ETo value is usually approached by an empirical method using weather data input. The recognized standard method for its reliability and can be used universally in determining ETo values is the FAO Penman-Monteith method. However, the use of this method is only possible if complete weather data is available. This study modified the simplest ETo calculation method, the Thornthwaite method and the evaporation pan method to obtain ETo values as accurate as FAO PM resulted. Callibrations are made by finding the correction number to get the best results shown by the high of correlation number and the efficiency index value. The results obtained are for the area with limited weather data condition, the Thornthwaite method both before and after calibration has better accuracy than the evaporation pan method. While the calibration carried out successfully increased the correlation number and efficiency index of both methods significantly. The results of the two calibrated methods, the Thornthwaite method provides better and satisfactory performance with a ratio between 0.86 and 0.89 and the efficiency index reaches 0.78.

Potensi lahan kering yang berbukit perlu dikembangkan untuk usahatani lahan terbatas guna terjadi pemerataan ketahanan pangan diberbagai wilayah yang potensial. Banyak lahan kering yang ada terutama pada daerah yang berbukit dan berlereng belum dikelola optimal untuk pertanian karena terbatasnya dukung teknik irigasi yang praktis. Pemanfaatkan perbedaan elevasi lahan yang ada merupakan potensi yang dapat dimanfaatkan oleh Teknik irigasi yang membutuhkan tekanan air. Teknik irigasi sistem pipa perforasi memiliki kesamaan dengan sistem sprinkler mini karena menggunakan tekanan air, dan sangat mungkin dapat diterapkan pada kondisi lahan berlereng, akan tetapi kemampuan sistem perforasi yang perlu diketahui lebih lanjut agar dapat dimanfaatkan untuk irigasi yang praktis. Untuk itu perlu dilakukan uji sistem irigasi perforasi dengan variasi kemiringan tertentu terhadap besarnya jangkauan pancaran dan keseragamannya, agar nanti dapat digunakan sebagai acauan awal.Model uji menggunakan sumber air dari tendon setinggi 3.7 m dan dengan tangki kapasitas ± 200 liter. Diameter pipa transmisi ½ inch dengan panjang 2.55 meter, dan  pipa lateral sebagai pipa perporasi dengan lubang 3mm terdiri dari 3 pipa dengan panjang pipa 4 meter diameter 1/2 inch dan jarak antar lubang pipa perporasi 0,60 m. Uji dilakukan terhadap 4 variasi kemiringan 10º, 20º, 30º dan 40º dengan 4 variasi head 1= 2.855 m, head 2 = 2.35 m, head 3 = 1.85 m dan head 4 = 1.30 m. Berdasarkan hasil penelitian menunjukkan bahwa, semakin besar kemiringan pipa transmisi maka head yang dihasilkan semakin tinggi. Keseragaman irigasi perforasi terjadi semakin kecil jika kemiringan semakin besar dengan nilai minimum 85% dan tertinggi 91%. Pancaran perforasi yang besar diperoleh pada kemiringan transmisi 20º dan 30º yaitu 2.66 m dan 2.40 m.

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This study aims to evaluate the ability of the ECHAM5 GCM model output data in estimating monthly rainfall on the island of Lombok. The data used in this study are ECHAM5 monthly rainfall data and automatic rainfall recorder (ARR) measurement rain data for 2000-2018 obtained from ARR Gunung Sari. Correction of bias is conducted by using the mean ratio method and the regression method. The method that produces the best approach is then used to obtain rain data projections and a simple regression method. Evaluation and validation used the Pearson correlation coefficient (r), Root Mean Square Error (RMSE) and Nash-Sutcliffe Efficiency (NSE) values. The results obtained are that the daily and monthly rainfall data from the ECHAM5 model cannot be directly used to replace the rain measurement data because of its very low accuracy. The downscaling technique performed on daily and monthly rainfall data using the average ratio method does not show satisfactory performance where the efficiency figures produced are still low even gave a slight increasing number. However, the ECHAM5 model data can be used to obtain rainfall projections on a monthly and seasonal scale with a good and satisfactory correlation.  Key words: mean ratio method; global climate model; ECHAM5; monthly rainfall.