Using a spatio-temporal dynamic state-space model with the EM algorithm to patch gaps in daily riverflow series, with examples from the Volta Basin, West Africa

International audienceA spatio-temporal linear dynamic model has been developed for patching short gaps in daily river runoff series. The model was cast in a state-space form in which the state variable was estimated using the Kalman smoother (RTS smoother). The EM algorithm was used to concurrently estimate both parameter and missing runoff values. Application of the model to daily runoff series in the Volta Basin of West Africa showed that the model was capable of providing good estimates of missing runoff values at a gauging station from the remaining series at the station and at spatially correlated stations in the same sub-basin

Effect of seasonal dynamics of vegetation cover on land surface models: a case study of NOAH LSM over a savanna farm land in eastern Burkina Faso, West Africa

International audienceThe sensitivity of the land surface model of the National Centers for Environmental Prediction (NCEP), the Oregon State University, the Air Force and the Hydrologic Research Lab (NOAH LSM) was evaluated with respect to the seasonal dynamics of the vegetation cover in the savanna area under intensive agriculture in the eastern part of Burkina Faso, West Africa. The data collected during the first long-term measurement of the surface fluxes in this mentioned region was used for this purpose. The choice of NOAH LSM was motivated by the fact that it has already been tested in different environments in West Africa, especially in Ghana. The sensitivity was tested by comparing the simulated surfaces fluxes using a fixed values of the roughness length for momentum as a standard in the model and the true seasonal value of this variable. The results show that NOAH LSM was not sensitive to the change of the roughness length for momentum neither on a seasonal basis nor on a daily basis, which was found to be abnormal. The formulation of the coefficient (Bc) coupling the dry canopy transpiration to the atmosphere was found to be the main reason for this. An improved formulation for this coefficient was given to solve this insensitivity and to improve the performance of the model. Recommendations are also given to enhance the performance of the model in the West African savanna environment

Corrélation entre les flux de chaleur sensible et latente avec la longueur de rugosité de surface. Influence sur la disponibilité des ressources en eau sur les terres intensivement exploitées de l’Est du Burkina Faso.

 L’exploitation des terres, exprimée par la longueur de rugosité de surface zo, est un facteur important qui influence le processus d’échange d’énergie entre la surface de la terre et l’air. Cette étude qui s’intègre dans le cadre des travaux de thèse intitulés « Impact de l’exploitation des terres sur le bilan hydrologique dans les bassins versants de l’Est du Burkina Faso » met en relation les principaux termes du bilan d’énergie (le flux de chaleur sensible et latente) avec la longueur de rugosité de surface zo calculée à l’aide de la loi de similarité de Moninh - Obhukoh.  La méthodologie est basée sur l’observation des données micro-météorologiques qui sont constituées des mesures simultanées des moyennes sur chaque heure de la vitesse du vent, du flux de chaleur sensible et latente et la température. Ces mesures ont été effectuées à 10 m du sol qui constitue la hauteur du mat de la station installée à l’Est du Burkina Faso précisément à Tanyele (département de Kompienga). Un anémomètre sonique triaxial est utilisé pour la mesure du flux de chaleur sensible, de la vitesse du vent et la température de l’air. L’hygromètre Campbell KH2O à krypton est utilisé pour la mesure du flux de chaleur latente. Le traitement des données brutes a été effectué par corrélation de remous en temps réel (chaque heure) à l’aide du logiciel ALTEDDY.  Les résultats montrent qu’il y a une bonne corrélation entre la longueur de rugosité de surface et les principaux termes du bilan d’énergie sur l’ensemble des données. Pour les données collectées sur une année, nous pouvons noter que le flux de chaleur sensible décroît exponentiellement lorsque la longueur de rugosité de surface croit (R2=- 0.84). De même le flux de chaleur latente croit de façon logarithmique avec la longueur de rugosité de surface (R2= 0.79). Lorsque nous analysons les données séparément sur les deux principales saisons qui caractérisent la zone d’étude (saison sèche et saison pluvieuse), nous constatons que la longueur de rugosité de surface n’a pas un impact significatif sur le flux de chaleur sensible et latente. D’autres paramètres climatiques tels que la radiation solaire, l’humidité relative et la température de l’air les déterminent. Cependant en saison pluvieuse, la longueur de rugosité de surface influence très négativement le flux de chaleur sensible (R2= - 0.92) contrairement au flux de chaleur latente qui montre une décroissance qui n’est pas aussi significative (R2= - 0.49). Cette décroissance du flux de chaleur sensible avec la longueur de rugosité de surface en saison pluvieuse peut entraîner une bonne recharge de la nappe si les écoulements de surface ne sont pas assez importants. Nous aurons besoin de beaucoup plus de données pour avoir des informations fiables sur la tendance croissante du flux de chaleur latente avec la longueur de rugosité de surface observée sur l’ensemble des données collectées

Critical scales to explain urban hydrological response: An application in Cranbrook, London

Rainfall variability in space and time, in relation to catchment characteristics and model complexity, plays an important role in explaining the sensitivity of hydrological response in urban areas. In this work we present a new approach to classify rainfall variability in space and time and we use this classification to investigate rainfall aggregation effects on urban hydrological response. Nine rainfall events, measured with a dual polarimetric X-Band radar instrument at the CAESAR site (Cabauw Experimental Site for Atmospheric Research, NL), were aggregated in time and space in order to obtain different resolution combinations. The aim of this work was to investigate the influence that rainfall and catchment scales have on hydrological response in urban areas. Three dimensionless scaling factors were introduced to investigate the interactions between rainfall and catchment scale and rainfall input resolution in relation to the performance of the model. Results showed that (1) rainfall classification based on cluster identification well represents the storm core, (2) aggregation effects are stronger for rainfall than flow, (3) model complexity does not have a strong influence compared to catchment and rainfall scales for this case study, and (4) scaling factors allow the adequate rainfall resolution to be selected to obtain a given level of accuracy in the calculation of hydrological response

The Influence of Rainfall and Catchment Critical Scales on Urban Hydrological Response Sensitivity

Interactions between spatial and temporal variability of rainfall and catchment characteristics strongly influence hydrological response. In urban areas, where runoff generation is fast due to high imperviousness degree, it is especially relevant to capture the high spatiotemporal rainfall variability. Significant progress has been made in the development of spatially distributed rainfall measurements and of distributed hydrological models, to represent the variability of catchment's characteristics. Interactions between rainfall and basin scales on hydrological response sensitivity, however, needs deeper investigation. A previous study investigated the hydrological response in the small urbanized catchment of Cranbrook (8 km2, London, UK) and proposed three dimensionless “scale factors” to identify if the available rainfall resolution is sufficient to properly predict hydrological response. We aim to verify the applicability of these scale factors to larger scales, with a distinct physiographic setting, in Little Sugar Creek (111 km2, Charlotte, USA), to identify the required rainfall resolution and to predict model performance. Twenty-eight events were selected from a weather radar data set from the National Weather Radar Network, with a resolution of 1 km2 and 15 min. Rainfall data were aggregated to coarser resolutions and used as input for a distributed hydrological model. Results show that scale factors and associated thresholds are generally applicable for characterization of urban flood response to rainfall across spatiotemporal scales. Additionally, application of scale factors in observation-based analysis supports identification of event characteristics that are poorly captured and critical improvements that need to be made before the model can benefit from high-resolution rainfall

Using a spatio-temporal dynamic state-space model with the EM algorithm to patch gaps in daily riverflow series

A spatio-temporal linear dynamic model has been developed for patching short gaps in daily river runoff series. The model was cast in a state-space form in which the state variable was estimated using the Kalman smoother (RTS smoother). The EM algorithm was used to concurrently estimate both parameter and missing runoff values. Application of the model to daily runoff series in the Volta Basin of West Africa showed that the model was capable of providing good estimates of missing runoff values at a gauging station from the remaining time series at the station and at spatially correlated stations in the same sub-basin

(89)Zr-Onartuzumab PET imaging of c-MET receptor dynamics

PURPOSE: c-MET and its ligand hepatocyte growth factor are often dysregulated in human cancers. Dynamic changes in c-MET expression occur and might predict drug efficacy or emergence of resistance. Noninvasive visualization of c-MET dynamics could therefore potentially guide c-MET-directed therapies. We investigated the feasibility of (89)Zr-labelled one-armed c-MET antibody onartuzumab PET for detecting relevant changes in c-MET levels induced by c-MET-mediated epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor erlotinib resistance or heat shock protein-90 (HSP90) inhibitor NVP-AUY-922 treatment in human non-small-cell lung cancer (NSCLC) xenografts. METHODS: In vitro membrane c-MET levels were determined by flow cytometry. HCC827ErlRes, an erlotinib-resistant clone with c-MET upregulation, was generated from the exon-19 EGFR-mutant human NSCLC cell line HCC827. Mice bearing HCC827 and HCC827ErlRes tumours in opposite flanks underwent (89)Zr-onartuzumab PET scans. The HCC827-xenografted mice underwent (89)Zr-onartuzumab PET scans before treatment and while receiving biweekly intraperitoneal injections of 100 mg/kg NVP-AUY-922 or vehicle. Ex vivo, tumour c-MET immunohistochemistry was correlated with the imaging results. RESULTS: In vitro, membrane c-MET was upregulated in HCC827ErlRes tumours by 213 ± 44% in relation to the level in HCC827 tumours, while c-MET was downregulated by 69 ± 9% in HCC827 tumours following treatment with NVP-AUY-922. In vivo, (89)Zr-onartuzumab uptake was 26% higher (P < 0.05) in erlotinib-resistant HCC827ErlRes than in HCC827 xenografts, while HCC827 tumour uptake was 33% lower (P < 0.001) following NVP-AUY-922 treatment. CONCLUSION: The results show that (89)Zr-onartuzumab PET effectively discriminates relevant changes in c-MET levels and could potentially be used clinically to monitor c-MET status

Zr-89-pembrolizumab biodistribution is influenced by PD-1-mediated uptake in lymphoid organs

Background To better predict response to immune checkpoint therapy and toxicity in healthy tissues, insight in the in vivo behavior of immune checkpoint targeting monoclonal antibodies is essential. Therefore, we aimed to study in vivo pharmacokinetics and whole-body distribution of zirconium-89 (Zr-89) labeled programmed cell death protein-1 (PD-1) targeting pembrolizumab with positron-emission tomography (PET) in humanized mice. Methods Humanized (huNOG) and non-humanized NOG mice were xenografted with human A375M melanoma cells. PET imaging was performed on day 7 post(89)Zr-pembrolizumab (10 mu g, 2.5 MBq) administration, followed by ex vivo biodistribution studies. Other huNOG mice bearing A375M tumors received a co-injection of excess (90 mu g) unlabeled pembrolizumab or(89)Zr-IgG(4)control (10 mu g, 2.5 MBq). Tumor and spleen tissue were studied with autoradiography and immunohistochemically including PD-1. Results PET imaging and biodistribution studies showed high(89)Zr-pembrolizumab uptake in tissues containing human immune cells, including spleen, lymph nodes and bone marrow. Tumor uptake of(89)Zr-pembrolizumab was lower than uptake in lymphoid tissues, but higher than uptake in other organs. High uptake in lymphoid tissues could be reduced by excess unlabeled pembrolizumab. Tracer activity in blood pool was increased by addition of unlabeled pembrolizumab, but tumor uptake was not affected. Autoradiography supported PET findings and immunohistochemical staining on spleen and lymph node tissue showed PD-1 positive cells, whereas tumor tissue was PD-1 negative. Conclusion Zr-89-pembrolizumab whole-body biodistribution showed high PD-1-mediated uptake in lymphoid tissues, such as spleen, lymph nodes and bone marrow, and modest tumor uptake. Our data may enable evaluation of(89)Zr-pembrolizumab whole-body distribution in patients