 In recognition of WEAP's 35th anniversary and of reaching the milestone of 50,000 users, we offer a retrospective of important steps in the evolution of WEAP, highlighting several important features. My name is Jack Sieber, and I have been managing the development of WEAP here at SEI for the past 31 years. Throughout the past 35 years, we have been continually improving WEAP, adding capabilities and features, increasing speed and robustness, improving the website and training materials, and expanding connections with users worldwide. While this video is very fast-paced, we will post it on our website so that you can view it again at your own pace. WEAP was initially developed in 1989 by the Stockholm Environment Institute for its internal use. SEI released the first public version in 1991. In the days before Microsoft Windows or the Internet, these early versions were DOS-based with barely any graphical user interface and only rudimentary data controls, tables, and charts. Nonetheless, WEAP provided a structured approach to integrated demand supply analysis. The first application modeled the rapidly diminishing ARL-C, along with policy scenarios for potential remediation. The following screens show the look and feel of these early versions, including drop-down menus, data screens, tables, and charts. The schematic was built as a list, not spatially explicit. There was only one main river, and only it could have tributaries. Result visualizations were fairly limited. By the late 90s, WEAP had created a graphical drag-and-drop interface to build the schematic, although there were no background layers, shapefiles, or ability to zoom in and out. Result visualizations had improved, including an overview with multiple charts. In these screenshots, you can see how the interface has changed and improved. In 2000, SEI created the first Windows version, with a GIS-based interface for creating the schematic, sophisticated data expression language for building models, and a linear program solver for allocating demands and supplies across multiple levels of rivers and tributaries. Beyond a simple accounting framework for demands and supplies, it included a physically-based hydrology for simulating rainfall runoff and infiltration, and modules for financial planning, water quality, and wastewater reuse. Results could be displayed on the map, and the interface was translated into French, Korean, Chinese, Spanish, and Portuguese. WEAP can display most of its results on the schematic. This can provide an easy way to visualize how results vary across time and space. Here we can see how the relative magnitude of the various demands and how they vary within each year and across years. Including transmission and return flows shows which supplies are active, and finally, including stream flow makes it clear the major flows in the system. Over 80 volunteers have helped translate the WEAP software and website into 28 different languages. This has helped make it easier to use and more accessible around the world. In the late 2000s, WEAP gained links to external models for groundwater, mod flow, and water quality, Qual2k, and an application programming interface, or API, enabled scripting in Python, JavaScript, or Visual Basic to automate WEAP or build linkages to external models and software. Modules were added for rice paddies, infiltration basins, and retention ponds, and combined sewer overflow, and translations for Arabic, Farsi, Russian, and Thai. In addition to its built-in groundwater model, WEAP could be linked to the widely used USGS mod flow groundwater model with connections to WEAP's demand sites, catchments, groundwater nodes, rivers, and reservoirs. Here you can see a 3D representation of groundwater levels at a high spatial resolution. The 2010s brought many important changes to WEAP, which you can see listed here. WEAP's scenario explorer presents a high-level overview of your model. Think of it as a dashboard with controls and gauges where you can control key model inputs and instantly see how those changes affect results. The user creates the dashboard by adding the most important inputs and outputs. Here we are looking at the sensitivity of the results to reservoir size in the Weeping River Basin. We can easily create new scenarios for smaller and larger reservoirs and compare them to the original scenario. For integrated water energy nexus studies, WEAP can be linked to LEAP, SEI's energy planning software. This simple example explores connections with hydropower, water sector electricity demands, and electricity sector water demands. Data and results can flow in a feedback loop between the two models, providing insights only available in a combined model. WEAP can export schematics and results to Google Earth. This provides a powerful and convenient way to package the results from a WEAP analysis to share with others. Each element is clickable, showing any notes from WEAP. Everything is saved in one file that can be sent via email or posted on a website for others to download and open in Google Earth. Results can be exported in two formats, as slides in an animation, or as individual charts for each schematic element. The user chooses which results to include for export for each element. Here we see supply requirements on unmet demand and reservoir levels. The late 2010s saw another batch of very significant changes shown here, perhaps the most important being automatic catchment delineation. WEAP can automatically delineate catchments and rivers using digital elevation data, calculate land area disaggregated by elevation band and land cover, and download climate data for each catchment and elevation band. This greatly simplifies the process of setting up and modeling catchment hydrology. WEAP automatically downloads global data sets for elevation, land cover, and climate as needed. The user can also use their own data sets for land use or climate. WEAP calculates the spatially weighted average for each user-defined elevation band for each climate variable. Here we can see how precipitation, temperature, relative humidity, and wind speed differ by elevation, as well as variation within each year and across years. It is easy to later modify your choices, such as subdividing the basin into different catchments, changing pour points or river head flow locations, or changing which climate or land use data set to use. WEAP will recalculate area and climate based on the new boundaries. In this case, we subdivided the Sacramento basin into two catchments, representing the two major sub-watersheds in the basin. Here are the major changes so far in the current decade. WEAP now includes access to the latest CMIPS-6 global gridded climate scenarios, representing daily climate projections out to 2100 for 27 global climate models and four shared socioeconomic pathways. The automatic catchment delineation can automatically download and apply any of these 108 data sets, spatially averaging them for each catchment and elevation band. This makes it very easy to build scenarios comparing multiple possible future climates. WEAP can automatically create a new shapefile that summarizes the climate for each climate grid square in your basin. The summary includes monthly and annual averages for each climate variable. The layer is added as a background layer on the schematic. By displaying a summary attribute as a thematic map, for example, average temperature or precipitation, you can quickly see how the climate varies across the basin. Show info charts to see all months for the location under the mouse. WEAP can calculate scenarios in parallel to greatly speed up calculations. In this demo, we are calculating 16 scenarios, four in each of the four separate copies of WEAP. Once each copy is finished calculating, it sends the results back to the main instance of WEAP for display. WEAP can automatically download and display background maps from several internet sources, such as USGS, OpenStreetMap, Google, National Geographic, and Esri. These include satellite images, street maps, and topographic maps, and can be very helpful when building your WEAP model. Once you have chosen a layer, you can pan and zoom on the schematic, and WEAP will download and display the background tiles. While we have always been driven in our WEAP development by user needs, we do also have our own ideas for future improvements. While my to-do list is nearly endless, major tasks include the ability to publish the scenario explorer view to web-based dashboards for online exploration, collaborative model building for teams like Google Docs, help streamline and automate our robust decision-support stakeholder process, increased access to public databases such as soil, climate, water demands, and reservoirs, and building serious games for interactive, WEAP-based simulations with stakeholders. We are currently working to move WEAP's scenario explorer to the web, where online visitors could see how changing data assumptions might impact results without the need to install WEAP on their computer. Over the past 35 years, more than 1,000 papers using WEAP have been published by SEI and other researchers. Here is a simple spatial analysis of many of those publications. And finally, I want to thank all the people and institutions that have supported and used WEAP over the past 35 years, including developers, collaborators, funders, trainers, translation volunteers, and everyday users. WEAP would not be as powerful or as easy to use as it is today without your help and feedback.