Regional Models Lake Victoria Model Prepared by C. Tubbs, P. Davies, Met Office UK Revised, delivered by P. Chen, WMO Secretariat SWFDP-Eastern Africa Training Workshop Bujumbura, Burundi, November 2013

MINISTRY OF WATER, LANDS AND ENVIRONMENT, DEPARTMENT OF METEOROLOGY, P.O. BOX 7025, KAMPALA UGANDA Mobile Weather Alert - Uganda Pilot

Lake Victoria - motivation Major convective storms driven by lake/land differences in temperature over Lake Victoria are believed to contribute to an estimated several thousand deaths each year of fishermen and small boat operators. A collaboration between WMO Uganda Department of Meteorology (UDoM) and other partners has been implementing a ‘Mobile Weather Alerts’ project to help address this danger. As a contribution to this project the Met Office has developed a 4km model over the Lake Victoria region.

© Crown copyright Met Office Incidents on Lake Victoria in kids drown in Lake Victoria “…preliminary reports have it that the boat was over-loaded and there were strong winds at the area.” Daily News, Tanzania, 5 August Feared dead on Lake Victoria “The period between April and September is tough for fishermen on the lake due to the strong winds and turbulent waves.” Daily Monitor, Uganda, 22 July Passengers feared dead as boat capsizes “Local fishermen were quick to attribute the incident to a storm, locally known as “nyakoyi”, that engulfed the lake, forcing the boat to capsize.” Daily Nation, Kenya, 1 November 2010

© Crown copyright Met Office The latest weather and climate science High resolution weather forecast models Satellite Observations

© Crown copyright Met Office Tailoring forecasts to the needs of fishermen ALERT STATE: GREENYELLOWORANGERED Mean Wind 0 – 5 KT6 – 10 KT11 – 20 KTOver 20 KT Wind gusts 5 – 10 KT11 – 20 KT21 – 30 KTOver 30 KT Thunder- storms LightModerateStrongSevere Visibility> 1Km500 – 1000m100 – 500m< 50m Hazard threshold: Very Low Low Moderate High Advice NilBe Aware Be Prepared Take Action Courtesy: Paul Davies, Met Office

© Crown copyright Met Office 2011 © Clare Wise de Wet Launch of the Mobile Weather Alert Service

Lake Victoria Model

Lake Victoria – model summary Initial model fields are downscaled (no data assimilation) from the 25km global configuration of the Met Office Unified Model (UM) to a 4km (0.036°), 70 level, partially convection-resolving configuration of the UM over the Lake Victoria basin. The model lid is at a height of 40km and the timestep is 100 seconds.Met Office Unified Model The model runs twice per day (by 0000UTC, 1200UTC), out to T+48. Lake surface temperatures are taken from the OSTIA model, which uses satellite measurements to produce a daily analysis of global lake and sea- surface temperatures.OSTIA Soil moisture is interpolated from an earlier global analysis. Daily forecasts from both cycles of the Lake Victoria model are available from

Lake Victoria – model science Science configuration currently follows that of latest Met Office UK4 and Euro4 4km 70 level operational NWP configurations.operational NWP configurations Uses the JULES land surface scheme.JULES There is no data assimilation, due to lack of in situ observations in the region. 4km resolution allows partially-resolved convection - resolved deep, parametrized shallow. Lower model resolutions, e.g. 12km, are fully parametrized. Higher resolutions, e.g. 1.5km, can be fully explicit/resolved.

Lake Victoria – strengths and weaknesses High-resolution orography represents local topography well, which improves surface temperatures and orographic precipitation. 4km models can begin to resolve convective activity and produce better (higher) peak precipitation, compared with lower resolution models. However, 4km not as good as 1.5km (UKV has fully explicit convection). Onset of convection is too slow as early small-scale stages of convection cannot be resolved, resulting in too few cells that are too large and too intense. Land-lake breezes and day/night differences in convection are represented, i.e. convection usually only over lake at night due to convergence. General pattern of convective cells can look “realistic” but detail of cell location/number/size cannot be assumed to be accurate.

Lake Victoria - orography Model orography is at a resolution of 4km, generated from Globe30 data. Lake Victoria and the surrounding 8 largest lakes are included in the domain (see lake temperature slide). Height of orography (m)

NWP convection switched on….

NWP convection switched off….

Lake Victoria – lake temperatures Lake surface temperatures are based on satellite measurements. These are ingested by the OSTIA model to produce a daily high- resolution global analysis of lake and sea-surface temperatures.OSTIA The “foundation temperature” that is produced is valid for a 24 hour period. Lake temperatures do not change through the forecast period. If observations are missing, lake temperatures are relaxed to climatological values. Lake surface “foundation” temperature (K)

Lake Victoria – soil moisture Soil moisture content (on 4 model levels, covering a depth of 3 metres) is interpolated to 4km resolution from the earlier global model analysis. Soil moisture content (kg/m2)

Lake Victoria Validation of model: Case study 17 th December km modelGlobal model Observations MSG Satellite OLR 17/12/ UTC T+18 forecast The global model was able to indicate that some event might take place, but the 4km model was able to add detail to the case and increase forecast confidence The 4km model is able to represent fine scale processes in a more explicit way. Due to the size of the grid points, it is also able to represent small scale events in more detail than the global model We still need skill in the global model as the 4km relies on it for large scale forcing

Global UM 4km UM 4 th March 2012: Storm over Lake Victoria caused the deaths of 2 fishermen when a boat capsized The Global UM showed some indication of the event in T+6 forecast The 4km UM showed increased indication of the storm in T+6 forecast Lake Victoria Validation of model: Case study 4 th March 2012

Objective analysis (automated ‘storm’/ ‘no storm’ decision made by an algorithm) was conducted on model data from February and March 2012 The 4km model was able to capture more storms than the global model The 4km model especially ‘added value’ at longer lead times hour forecasts, though it did add some more false alarms. Good forecasts are always a balance between getting fewer false alarms without getting more missed events Lake Victoria Validation of model: Objective analysis SHORTER LEAD TIME LONGER LEAD TIME

Lake Victoria – future plans Lake temperatures – in future OSTIA developments, diurnal variation and in situ lake temperatures may be added. Model science – investigations into whether forecast performance can be improved for the tropics, with adjustments to the model settings (e.g. turbulence scheme). Lightning forecasting capability will be trialled. Web – website will be updated shortly, with more interactive model and satellite imagery.website