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Leaf phenology in tropical deciduous forests significantly influences water and carbon exchanges between vegetation and the atmosphere. Thus, a comprehensive understanding of the effects of hydrometeorological variables on the growing period is essential for predicting plant water use following climate change. We investigated whether leaf phenology, bud break, and leaf abscission in mature deciduous teak trees (Tectona grandis L. f.) were induced by the root zone soil moisture content. Using heat pulse velocity and photographic imagery, we compared the deciduous periods (DPs) of two teak trees under natural conditions and two underirrigated conditions. DPs ranged from 47 to 84 days under natural conditions, whereas irrigation shortened the DP by approximately 2 weeks and promoted high levels of water use for 10 months. Thus, the annual water use of irrigated trees far exceeded that of control trees. Under irrigated conditions, leaf abscission and reduced water use were accelerated when the daily mean vapor pressure deficit exceeded 14 hPa following a period of gradual senescence. This study presents preliminary results regarding the impact of irrigation on the teak tree DP. However, uncertainty remains due to insufficient replication; thus, further tests are needed. Nonetheless, our results may predict leaf phenology after short dry periods. Key words: deciduous period, heat pulse velocity, irrigation, relative soil moisture, teak (Tectona grandis). La phenologie foliaire dans les forets tropicales decidues a une influence significative sur les echanges d'eau et de carbone entre la vegetation et l'atmosphere. Par consequent, une comprehension exhaustive des effets des variables hydrometeorologiques sur la periode de croissance est essentielle pour predire l'utilisation de l'eau par les plantes a la suite des changements climatiques. Nous avons cherche a savoir si la phenologie foliaire, le debourrement et l'abscission des feuilles chez les tiges matures de teck (Tectona grandis L. f.), une espece decidue, etaient induits par la teneur en humidite du sol dans la zone des racines. A l'aide de la methode basee sur la vitesse de deplacement d'une impulsion de chaleur et de l'imagerie photographique, nous avons compare les periodes decidues (PD) chez deux tiges de teck qui etaient irriguees et deux autres qui ne l'etaient pas. La PD variait de 47 a 84 jours sans irrigation tandis que l'irrigation a ecourte la PD d'environ 2 semaines et favorise un niveau eleve d'utilisation de l'eau pendant 10 mois. Par consequent, l'utilisation annuelle de l'eau par les arbres irrigues a largement depasse celle des arbres temoins. Chez les arbres irrigues, l'abscission des feuilles et l'utilisation reduite de l'eau ont ete accelerees lorsque la moyenne journaliere du deficit de saturation excedait 14 hPa a la suite d'une periode de senescence graduelle. Cette etude presente des resultats preliminaires concernant l'impact de l'irrigation sur la PD du teck. Cependant, l'incertitude demeure a cause du manque de repetitions; par consequent, d'autres tests sont necessaires. Neanmoins, nos resultats peuvent predire la phenologie foliaire apres de courtes periodes de secheresse. [Traduit par la Redaction] Mots-cles: periode decidue, vitesse de deplacement d'une impulsion de chaleur, irrigation, humidite relative du sol, teck (Tectona grandis)., Introduction Events related to leaf phenology in tropical deciduous forests, including bud break, leaf growth, and leaf abscission, significantly influence water and carbon exchanges between vegetation and the atmosphere. The [...]

Over most tropical land areas, the annual peak in precipitation occurs during summer, associated with the local monsoon circulation. However, in some regions of the tropics, the bulk of their [...]

Author(s): Mahyar Mohtadi (corresponding author) [1]; Matthias Prange [1]; Stephan Steinke [1] Monsoons are the dominant seasonal mode of climate variability in the tropics and are critically important conveyors of [...]

Byline: Theo Chidiezie Chineke (1), Shrikant S. Jagtap (2), Okechukwu Nwofor (1) Abstract: In July, heating of the continents in the Northern Hemisphere results in strengthened monsoon systems which bring rains to West Africa. In Nigeria, the annual rainfall total decreases from over 3,800 mm at Forcados on the coast to under 650 mm at Maiduguri in the north-east of the country. June, July, August and September are the rainiest months throughout the country. In many parts of the south, however, there is 'supposed to be' a slight break in the rains for some 2 to 3 weeks in late July and early August or the so called 'August break'. In this study, we are underscoring the obvious that climate is changing. The daily series of rainfall data for 1983--2003 analyzed between the months of July--August for some sites in the Eastern humid zone of Southern Nigeria shows that the 'August break' may indeed 'be breaking'. We have discussed some practical approaches to climate change research in this monsoon region. Author Affiliation: (1) Atmospheric Physics Group, Department of Physics, Imo State University, PMB 2000, Owerri, Nigeria (2) Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, 32605, USA Article History: Registration Date: 08/12/2009 Received Date: 26/09/2005 Accepted Date: 30/10/2009 Online Date: 21/01/2010

Using a high-resolution regional climate model--the Abdus Salam International Centre for Theoretical Physics Regional Climate Model version 3 (RegCM3)--and station and satellite observations, the authors have studied the spatial heterogeneity of climate variability over Java Island, Indonesia. Besides the well-known anomalous dry conditions that characterize the dry and transition seasons during an El Nino year, analysis of regional model output reveals a wet mountainous south versus dry northern plains in precipitation anomalies associated with El Nino over Java during the peak rainy season. Modeling experiments indicate that this mountains/plains contrast is caused by the interaction of the E1 Nino--induced monsoonal wind anomalies and the island/mountain-induced local diurnal cycle of winds and precipitation. During the wet season of El Nino years, anomalous southeasterly winds over the Indonesian region oppose the climatological northwesterly monsoon, thus reducing the strength of the monsoon winds over Java. This weakening is found to amplify the local diurnal cycle of land--sea breezes and mountain--valley winds, producing more rainfall over the mountains, which are located closer to the southern coast than to the northern coast. Therefore, the variability of the diurnal cycle associated with this local spatial asymmetry of topography is the underlying cause for the heterogeneous pattern of wet south/dry north rainfall anomalies during El Nino years. It is further shown that the mean southeasterly wind anomalies during December-February of El Nino years result from more frequent occurrence of a quiescent monsoon weather type, during which the strengthened sea-breeze and valley-breeze convergence leads to above normal rainfall over the mountains. DOI: 10.1175/2010JAS3348.1

Analysis of suspended sediment transport data for rivers in Yunnan and Tibet shows that monsoon flows control effective discharge. We calculate effective discharge, defined as the discharge that transports the most sediment, for 44 stations for which there is at least one complete year of daily suspended sediment concentration and mean daily discharge data, and find that the effective discharge is approximately the mean monsoon discharge for all stations. The correspondence of the effective discharges with the mean annual flow and monsoon discharge for all stations demonstrates that monsoon flow dominates suspended sediment transport in the region, rather than storm flow during discrete, short-duration storm events. In this region, the monsoon lasts for 4 months (June-September) and during that time transports 86% of the suspended sediment load. In contrast to the general observation from temperate environments that infrequent, stochastic storm events dominate sediment transport (with 90% of the suspended sediment transport occurring in 10% of the time), our findings show that the mean monsoon discharge dominates sediment transport in the rivers draining the southeastern Tibetan Plateau. doi: 10.1130/G31444.1