Landscape Irrigation Management Program IS005 Quick Answer

Transcription

1 Landscape Irrigation Management Program IS005 Quick Answer Copyright (2003) Regents of the University of Caifornia Created on November 15, 2003 Revised June 1, 2004 R. L. Snyder, Biometeoroogy Speciaist Department of Land, Air and Water Resources University of Caifornia Davis, CA 95616, USA S. Eching, Senior Land and Water Use Scientist Caifornia Department of Water Resources Office of Water Use Efficiency P.O. Box Sacramento, CA 94236, USA INTRODUCTION The Exce program LIMP.XLS is used to cacuate ET o rates, determine andscape coefficient (K L ) vaues, estimate andscape evapotranspiration (ET L ) and determine irrigation schedues. In addition, there is another Exce program DU.XLS, which is used to determine distribution uniformity of sprinker systems. Evapotranspiration from andscape vegetation is estimated by using a regiona measure of evaporative demand (ET o from the Caifornia Irrigation Management Information System or CIMIS), a microcimate coefficient (K m ) to estimate the ET o in a oca microcimate, a vegetation coefficient (K v ) that accounts for species differences in ET from we watered vegetation, a density coefficient (K d ) that adjusts the ET estimate depending on vegetation density, a stress coefficient (K s ) that adjusts for reductions in ET due to water stress and an evaporation coefficient (K e ) that defines a baseine coefficient vaue. Initiay, the coefficient (K w ) to estimate ET of a we-watered vegetated cover is estimated as: K = K K K w m v d

2 Then K w is mutipied by a stress coefficient (K s ) to adjust for reductions in ET beow that of we-watered vegetation. However, the evaporation coefficient is a baseine, so the andscape coefficient is cacuated as: K = K K > K w s e and the andscape evapotranspiration (ET ) is cacuated as: ET = ET K. o WEATHER WORKSHEET In the worksheet Weather, the upper tabe is used to estimate regiona daiy ET o rates by month and to enter the coefficients used to cacuate andscape ET (ET ). The ower tabe is used to input weather data representing the microcimate of the irrigation site to deveop monthy microcimate correction factors to estimate the Loca ET o rates. Either daiy mean ET o rates or weather data are input to estimate Regiona ET o rates in the upper tabe. Then LIMP uses a smooth curve fitting technique to estimate daiy ET o rates during the year from the monthy data. Weather inputs can incude the daiy mean (1) soar radiation (MJ m -2 d -1 ), air temperature ( o C), wind speed (m s -1 ), and dew point temperature ( o C). The program cacuates ET o using the Penman-Monteith (PM) equation (Monteith, 1965) as presented in the United Nations FAO Irrigation and Drainage Paper (FAO 56) by Aen et a. (1998) and using the Hargreaves-Samani (HS) equation (1982 and 1985). If ony temperature data are input, then the Hargreaves-Samani equation is used. For the ETo cacuations, the station atitude and eevation must aso be input. If the ces are eft bank, then atitude 0 o and eevation 0 meters above sea eve are used. Cimate data representing the Loca site are input in the ower tabe of the Weather worksheet and ET o is cacuated using the PM and HS equations. The ratio of oca over regiona ET o is computed and dispayed in the right-hand coumn of the ower tabe. This ratio represents a monthy caibration for microcimate. Whie the microcimate (K m ) factors are shown in the ower tabe, they are ony used by the program if they are copied to the right-hand coumn of the upper tabe using Copy Paste Specia Vaues. A smooth curve fitting procedure is used to estimate daiy K m vaues for the year. If no vaues are input into the right-hand coumn of the upper tabe, the defaut vaue of K m = 1.0 is used. The vegetation coefficient (K v ) is used to adjust ET for pant species differences from ET o (i.e., the ET of ta, coo-season grass). The K v coefficient represents a wewatered vegetation with a fu canopy. The K v accounts for morphoogica and physioogica differences between the vegetation and the reference surface (ET o ), but

3 adjustments for water stress are done with a stress coefficient (K s ). Therefore, K v accounts for differences in net radiation, turbuence due to surface roughness, and stomata differences reative to ET o, which is an approximation for coo season grass that is 0.12 m ta and we-watered. It is assumed that the pant physioogy changes itte during the year, so one vaue is used for K v a year. The K v vaue is input at the top of the Weather worksheet. Sparse canopies have ower ET than dense canopies of the same vegetation and a density coefficient (K d ) is needed for the adjustment. Since there is no known correction for andscape vegetation, the foowing correction for immature deciduous orchards is used to estimate K d in LIMP. K d CG π = sin 70 2 where C G is the percentage of ground covered by green growing vegetation. It is assumed that this reationship accounts for differences in ight interception by canopies with cover ess than 70 %. For canopies with more than 70 % cover, K d = 1.0. The percentage ground cover is input by month in the upper tabe of the Weather worksheet, the monthy K d vaues are cacuated and curve fitting is used to estimate the daiy K d vaues. If the ground cover ces are eft bank, the defaut vaue K d = 1.0 is used. Monthy stress coefficient (K s ) vaues are input into the upper tabe of the Weather worksheet. A coefficient of K s = 0 woud force ET = 0 and a K s = 1.0 impies no reduction in ET due to water stress. After entering the monthy data, daiy K s vaues are computed for the entire year using a curve fitting technique. In oder iterature, it was common to tak about water use differences between vegetation and a species coefficient was used to estimate the vegetation ET from ET o. However, in LIMP, the vegetation coefficient (K v ) is used to estimate the ET of vegetation with adequate water to not inhibit ET and the K s coefficient is used to estimate the ET when the vegetation is stressed. Bare soi evaporation is estimated for each day of the year using daiy ET o estimates and the number-of-rainy-days per month (NRD), which are input into the Weather worksheet. The NRD is used to estimate the days between rainfa for each month and the resuts are used with ET o to estimate bare soi evaporation (E s ) using a 2-stage mode. Then the estimated soi evaporation (E s ) is used to cacuate a daiy mean K e = E s /ET o vaue for bare soi for each month. Curve fitting is used to estimate daiy vaues of K e over the year. The K e is a baseine coefficient, so the K vaues must be greater than or equa to K e.

4 OUTPUT Daiy vaues from each of the coefficients is both potted in LIMP (charts Km_pot, Kd_pot, Ks_pot and K_pot) and isted in tabes (worksheets Km, Kd, Ks, Ke and K). The baseine coefficient K e is aso potted in K_pot. The OUTPUT worksheet contains a row of a coefficient and ET cacuations for each day of the year. SCHEDULING The LIMP program aso suppies information for irrigation scheduing. The worksheet RT is used to estimate the daiy sprinker runtime needed to repace the ET osses and account for appication efficiency. The appication rate and efficiency are input at the top of the worksheet and the runtime minutes to efficienty irrigate are dispayed in the tabe. When the appication area is input, the tota runtime hours and appication amount for the year are dispayed at the top of the tabe. The CRT worksheet shows the cumuative runtime minutes to repace ET osses during the year. If any character is input in the sma ce immediatey eft of a cumuative vaue, the cumuative runtime is reset to zero on that date and the runtime wi accumuate unti the end of the year. If one knows the maximum runtime possibe to avoid runoff, entering characters on dates with that runtime or ess wi provide a schedue during the year. The worksheet K_Mut is used to input the K vaues for up to 20 watering zones. To input the K vaues, create the K vaues for the vegetation of interest using the Weather worksheet and then copy the daiy K coumn from the OUTPUT worksheet to the appropriate coumn in K1_Mut. When a coumn of K vaues is copied to the worksheet, a coumn of runtime vaues is created in the RT_Mut worksheet. Then the appication rate and appication efficiency are input at the tops of the coumns in the RT_Mut worksheet. Assuming itte or no runoff, the distribution uniformity can be used to estimate the appication efficiency. The runtime needed to repace daiy water osses on each day of the year by zone is dispayed under the appication efficiency. The CRT_Mut worksheet provides the corresponding cumuative runtime requirements for each day of the year for each of the 20 zones. Entering any character in the bue coumn to the eft of the tabe wi zero the accumuation on the corresponding date and the runtimes wi begin to accumuate again on the foowing day. The LIMP program can determine runtimes needed for irrigation of urban andscape vegetation using daiy ET o cacuated from monthy cimate data. However, one can aso input the current ET o data into the ETo worksheet, which is just to the

5 right of the Weather worksheet. To change ET o vaues, cick on the ce to the eft of where data are to be changed and then enter the current ET o vaue. The program wi automaticay update a ET cacuations in the scheduing worksheets. DISTRIBUTION UNIFORMITY CALCULATION For the distribution uniformity cacuations, use the program DU.XLS. Catchcan data from a system evauation are input in the DU worksheet. The units are seected at the top. The catchcan opening diameter, sprinker runtime, and the voume or depth units for entering the voumes of water coected must be seected. The voumes or depths from each catchcan are input into the upper spread sheet and the distribution uniformity (DU) and appication rate (AR) are automaticay dispayed. The ow quarter of the catchcan containers receiving the east voume of water is highighted to show where the sprinker appications might be deficient. The input data are ranked from highest to owest and are potted in the chart rankpot. The mean of the ow quarter and the sampe mean are aso dispayed on the pot. When using the CRT_Mut worksheet of LIMP, input the appication rate and efficiency above the coumns. Use the DU from the system evauation as an estimate of the appication efficiency, which is aso input at the tops of the coumns. This is a vaid use of the DU as ong as there was itte or no runoff and the generated runtimes are used in the schedue. REFERENCES Aen, R.G., Pereira, L.S., Raes, D., and Smith, M Crop evapotranspiration Guideines for computing crop water requirements. FAO Irrig. and Drain. Paper 56. Food and Agricuture Organization of the United Nations, Rome. pp Hargreaves, G.H., and Samani, Z.A. (1982) Estimating potentia evapotranspiration. Tech. Note, J. Irrig. and Drain. Engrg., ASCE, 108(3): Hargreaves, G.H., and Samani, Z.A. (1982) Reference crop evapotranspiration from temperature. App. Engrg. in Agric., 1(2): Monteith, J.L Evaporation and the environment In the movement of water in iving organisms, XIXth Symposium. Soc. of Exp. Bio., Swansea, Cambridge University Press.