Latest Contributions by YacoubRaheem

Several authors have found a similar phenomenon to what you found, namely that rainfall from rain gauges correlates more strongly with coarse resolution elevation than high resolution. I am looking at rainfall patterns in South Africa and Mozambique and found that 20km DEMs actually correlated more strongly with rainfall than 1km, 5km, 10km, or 15km to average annual rainfall. I suggest a couple papers (you will probably need access to the journals in order for the weblinks to work): Prudhomme, C., and D. W. Reed (1998). Relationships between extreme daily precipitation and topography in a mountainous region: A case study in Scotland. International Journal of Climatology, 18, 1439-1453. http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-0088(19981115)18:13%3C1439::AID-JOC320%3E3.0.CO;2-7/pdf Ekström, M, P. C. Kyriakidis, A. Chappell, P. D. Jones (2007). Spatiotemporal Stochastic Simulation of Monthly Rainfall Patterns in the United Kingdom (1980�??87). Journal of Climate, 20, 4194�??4210. http://journals.ametsoc.org/doi/pdf/10.1175/JCLI4233.1 I have a few questions of my own... and I apologize in advance for so many of them. They sort of build upon one another, so I thought it would be easier to post them all together: I am looking at how ancillary terrain data (e.g., elevation, distance from large water body, slope, aspect) improves spatial interpolation of rainfall data from rainfall gauges. I have daily rainfall data but my dependent variable will be annual (or perhaps average annual or seasonal) rainfall. 1. Should I just be using ordinary cokriging (instead of simple or universal)? 2. There is a trend in the rainfall data. However, this trend is mainly due to elevation (and likely/hopefully some of these other ancillary terrain data). Thus, should I NOT detrend the data if I am going to cokrige with elevation and other data? 3. Following the geostatistical wizard, when performing semivariogram modeling, should I always click the Optimize Model button? When/why would I not want to optimize the model? 4. In general, optimizing produces improved results (in terms of prediction errors); however, there are few cases I have found when they don't. Do you know why that is? 5. Can I always use the prediction errors table as a guide for whether a model is improved or not? I realize the various prediction errors are providing different pieces of information (e.g. mean indicates level of bias; RMS indicates accuracy), however, if one piece of ancillary data improves the mean, for example, and cokriging with another piece of ancillary data improves the RMS, is there way to say that either piece of ancillary data is "better" than another? 6. Is there some pre-processing/analysis I should do before I get into cokriging with multiple pieces of data? I have developed cross-correlation tables with all my ancillary data, so in non-spatial terms I know which data are most highly correlated with rainfall. Are these definitely going to be the ones that also help to improve the model with cokriging or is there value in experimenting with ancillary data that aren't as highly correlated with rainfall? 7. Are there any in-built mechanisms for model selection criteria (e.g., AIC, BIC), in order to help determine which of my, say, 10 pieces of ancillary data are most appropriate for cokriging? 8. The Help Section on Cokriging says that "Theoretically, you can do no worse than kriging because if there is no cross-correlation, you can fall back on autocorrelation for Z1." However, there are times when some if not all the precision errors decrease when cokriging... and time when using two or three pieces of ancillary data for cokrining decreases the prediction errors more than just using one... Does this make sense? (Sometimes there is no change at all in the prediction errors when adding a second or third piece of ancillary data, and this makes sense, I suppose. I wonder if this could be determined apriori by just looking at the cross-correlation table.) 9. Is there a way to use the Geostatistical Wizard with model builder, or just some way to perform batch processing when I want to perform kriging with various combinations of ancillary data and compare prediction errors? 10. After I figure out which set of ancillary data best improves the model, I want to perform Gaussian Geostatistical Simulations in order to develop equally likely realizations of rainfall (for use in stochastic rainfall-runoff modeling)... I would like to use the ancillary data to help explain the trend as much as possible; next I want to perform simulations on the rainfall residuals; and finally I will add these residuals back to the trend. I haven't gotten to the simulations part yet, but I just noticed that it must be based only on a Simple Kriging model... does this mean I should be using simple kriging instead of ordinary kriging?... Or perhaps I'm comparing apples and oranges here... Perhaps my question should simple be: how do I combine cokriging with simulations? Perhaps the step I mentioned above about of first figuring out the trend then performing simulations on the residuals is not the way to think about it... THANKS!!!... and sorry so many questions!... (I'll owe you a beer at the UC this year!) Cheers, Yacoub ... View more

Check out my last post on: http://forums.arcgis.com/threads/8274-ArcHydro-in-ArcGIS-10?highlight=arc+hydro I had the same problem... Make sure the Data Frame has the same spatial reference as the DEM you are processing. In other words, make sure the DEM you will work on is the first layer that you Add when you open up a new map. If you are using ArcGIS 10, then I think this is the latest ArcHydro10: ftp://RiverHydraulics:river.1114@ftp.esri.com/ArcHydro/Setup10/ I was using HEC-GeoHMS10 (http://www.hec.usace.army.mil/software/hec-geohms/download.html), and when you install that, a slightly older version of ArcHydro10 automatically gets installed. I'm not 100% sure, but I think the newest version of ArcHydro10 is tiny bit less buggy when it comes to issues like the one you have. Good luck! Cheers, Yacoub ... View more

WOW!!! You guys are rock stars! Thank you so much for the support! The solution ended up being relatively simple... though of course it took me 8 hrs to finally narrow it down the problem! I started with an ASTER file. It was the first file I brought in so of course the data frame was set to that. I then opened toolbox from within ArcMap and projected the ASTER file. Then I ran the terrain preprocessing steps on that projected file... that was my problem. I needed to close ArcMap and first add the projected file, so that the Data Frame was in the spatial reference as the DEM I was processing. It seems like ArcHydro likes it when the data and the Data Frame are in the spatial reference. I guess its some issued related to reprojecting on the fly. Some of the other silly things I tried that actually seemed to sometimes help (it definitely does seem like ArcHydro is buggy...) are to NOT keep the data in the "C:\Documents and Settings\user\My Documents\ArcGIS" folder, and instead keep them in a folder right on the C drive. ArcHydro perhaps doesn't like file names and extensions with spaces. Also, for some reason I was getting errors when I was projecting into Africa Albers Equal Area Conic but NOT when I was projecting into UTM 37S (Mozambique). But that was actually only a problem with the ArcHydro version that installed when I installed HEC-GeoHMS 10, not when I installed the latest ArcHydro. Thanks again! I haven't posted on one of these forums in years and its great to know there is such immediate response! ... View more

Hi, I am running Windows XP Professional with Service Pack 3 (Pentium Dual-Core CPU, 3.07 GHz, 1.96 GB RAM). I have ArcGIS 10. I have installed the ArcGIS 10 Service Pack 3 (http://resources.arcgis.com/content/patches-and-service-packs?fa=viewPatch&PID=66&MetaID=1807). I installed what I thought was the latest version of ArcHydro 10 version 2.01.133 from here: ftp://RiverHydraulics:river.1114@ftp.esri.com/ArcHydro/Setup10/. I am delineating watersheds from 30m ASTER DEMs. I go through the standard pre-processing steps (Fill Sinks, Flow Direction, Flow Accumulation, Stream Definition, Stream Segmentation, Catchment Grid Delineation, Catchment Polygon Processing). Then I get to Drainage Line Processing and I get the following error: Error HRESULT E_fail has been returned from a call to a COM component. I tried uninstalling ArcHydro and then installing HEC-GeoHMS 10.0 (http://www.hec.usace.army.mil/software/hec-geohms/download.html) which automatically installs ArcHydro10 version 2.0.1.125. When I go through the same process, I get the same error. This does not happen when I run this on Windows 7 machine (Intel Core i5, 2.53 GHz, 4GB Ram, 64-bit OS). I am mainly a user and not so much a developer... Please help!!! Thank you, Yacoub email: yacoub@stanford.edu ... View more