Vivien S. Esquivel
The reliability of our water resources is of today’s great concern. An assessment would be of great help to water resources managers and policy makers in that it would show the changes in the efficiency of the present water resource systems under extreme climate events like El Niño and La Niña.
A statistical analysis was undertaken in this study, relating the behavior of inflows of Angat and Magat water reservoirs with the corresponding El Niño indices i.e., sea surface temperature anomalies (SSTA) and Southern Oscillation Index (SOI).
Standardized monthly inflow anomalies from April to March of the following year to concide with the rain-year were averaged and plotted in a time series to show the general relationship between inflow and the corresponding sea surface temperature anomalies and Southern Oscillation Index. With Angat water reservoir, four (4) negative anomalies were experienced out of the six (6) El Niño episodes and two (2) positive anomalies. On the other hand, five (5) out of six (6) La Niña episodes exhibited positive anomalies and one (1) negative anomaly. Magat water reservoir experienced four (4) negative anomalies during the six (6) El Niño events and four (4) positive anomalies during the six (6) La Niña events.
To examine further the effects of ENSO, continuous monthly-standardized inflow anomaly data from 1970 to 2002 observed in Angat and Magat water reservoirs were also assembled in a time series. These data were lag correlated from 0 to 12 months with the corresponding SSTA and SOI averages and found to have consistent negative values with SSTA and the opposite with SOI. SSTA’s strongest relationship with inflow is on the 4th month lag time and SOI’s strongest relationship with inflow is on the 3rd month lag time. These relationships refer to both reservoirs. Magat exhibited higher correlation values than Angat.
Composites for a 36-month period of each El Niño and La Niña events were also presented to show the magnitude of inflow anomalies during these extreme climate events. El Niño composites were centered at the peak of SST positive anomaly, while La Niña composites were centered at the peak of SOI positive anomaly. Negative inflow anomalies on both reservoirs are significant during El Niño years. La Niña years did not cause much impact on inflow anomalies and their effects are comparable to normal years.
Cynthia P. Celebre
Terrain-induced meso-scale circulations such as sea and mountain breezes occurring over Metro Manila were examined. The study involved observational as well as theoretical phases.
The observation stage that was undertaken on 14-16 May 2002 aimed to use the gathered data to initialize and validate the model as well as determine the variations of the structure of the lower atmosphere during the daytime. During the study period, NAIA, Port Area, and Science Garden synoptic stations were used. The PAGASA Astronomical Observatory was temporarily employed by installing instruments that observed relative humidity, dry bulb temperature and wind speed and direction. The radiosonde mobile van of the Natural Disaster and Research Branch (NDRB) of PAGASA was also employed. A simultaneous three-hourly release of pilot balloons was also made at the PAGASA Astronomical Observatory and the Planetarium in Rizal Park in Manila. A vehicle moving every hour from 8AM to 5PM from Quirino Grandstand towards inland was also part of the observation program.
Analyses of specific humidity, temperature and wind speed and direction showed that Port Area was frequently affected by sea breeze although the circulation penetrated inward up to the vicinity of the PAGASA Astronomical Observatory. Onset of sea breeze in NAIA was difficult to determine due to the effect of Manila Bay and Laguna de Bay on the area.
The second segment applied the Advanced Regional Prediction System (ARPS) numerical model that was developed by the Center for Analysis and Prediction of Storms (CAPS) of the University of Oklahoma, U.S.A. It was utilized to simulate the meso-scale circulations occurring over the domain during the day.
The ARPS Version 4.0 was implemented for the entire Metro Manila Area including the Manila Bay and Laguna de Bay. With a 2-km grid spacing, the horizontal domain had 55 x 55 grid points spanning about 110 km x 110 km (1° latitude x 1° longitude). The study made use of the three-dimensional Cartesian geometry (X, Y, Z) with 80-grid points and 200 m grid distance in the vertical.
Six experiments were designed to determine the effects of various factors such as wind speed, wind direction and land use on a flat or with terrain domain, in the development of terrain-induced meso-scale circulations. The results of these experiments showed that for a flat domain, rainfall occurred near the urban area for low wind speed. Increasing the wind speed caused the rainfall to move farther from the urban area but no rainfall was observed for the maximum wind speed used. The amount of accumulated rainfall, was greatest for the lowest wind speed. It was also observed that changes in the wind direction caused changes in the location of cloud and rainfall formation.
For a domain with terrain, it was observed that the urbanization effect with respect to temperature was not evident in all simulations since cloud and rainfall were observed near the mountain. Accumulated rainfall increased for the 2 m/s wind but no rainfall was also noticed for the 5 m/s wind speed.
A late formation of cloud was observed when only rural and water surfaces were utilized instead of also including an urban area as land use. Results also displayed that cloud and rainfall occurrences were located at the eastern most section of the domain.
Nestor B. Nimes
Series of experiments are conducted to demonstrate the effect of moving storm rainfall over a catchment such as the Angat basin. Four (4) years of hourly rainfall accumulation from three (3) gaging locations in the study area comprise the dataset used in the study. First and second order moments (mean, variance, auto-covariance and cross-covariance) are evaluated and used to establish the different parameters of the Neyman-Scott stochastic, space-time rainfall model. The model is based on clustering principle in storms and the random characteristics of storm rainfall. The parameters are established by the application of the Newton-Raphson Iterative Non-Linear Least Squares and the Fletcher-Reeves Conjugate Gradient methods for optimization.
Rainfall fields are generated with specified storm direction of movement and at different speeds. Eight (8) cardinal directions and five (5) storm speeds are applied and produced seventy two (72) hours of rainfall traces in various amounts and spatial distribution over the basin.
The effect of moving storm rainfall is investigated by the application of the National Weather Service-PC version model (NWS-PC) in the simulated runoff hydrographs based on the stochastically generated rainfall data, soil data and basin characteristics as input. Corresponding inflows are investigated in terms of times to peak, peak discharges and total volumes.
Results show that most of the maximums of the rainfall fields generated are located at the exit of the storms except the one coming from the south, where the maximum of the rainfall field is located in the east side instead in the north. This finding shows a notable variability in the location of maximums in the rainfall field at different directions. The variation in the total maximum generated rainfall at different directions is range from 195 mm. to 240 mm. This variation at different directions of storm may be small, but cannot be disregarded. Apparently, the variation in the pattern of minimum and maximum values in the rainfall field is significant on the distribution of the rainfall field, in its location and its spatial distribution. The findings mentioned above, indicate that at different storm directions influence the spatial rainfall distribution, while different speeds affect considerably the magnitude of rainfall over the basin.
The investigation shows that the variations on the times to peak both in the direction and speed are quite considerable at the 50% CDF but not at the 90% CDF. There are significant variations in the times to peak in the 10 kph and 20 kph speeds based on different directions, while other speeds have no indication of variations. The slower storms generated large amount of rainfall than the faster storms in all directions. In slower storms, the peak discharges and the corresponding total volumes are higher than the faster storms in all directions. Hence, the storm movements have significant effect on inflow in the Angat reservoir and cannot be neglected in proper evaluation and assessment for dam operation.
The Neyman-Scott stochastic, space-time rainfall model is recommended for hydrologic simulation studies because of its capability to capture the rainfall physical structure and characteristics, and its ability to capture the space-time structure of the rainfall process. Likewise, the National Weather Service PC version model for runoff simulation is also recommended because it can run fast on desktop computers both in calibration and simulation mode. Moreover, it is flexible in its input, parameterization and output operation and can be applied in any type of basin.
Shirley J. David
The study made use of the first-order three-state Markov chain process to characterize rainfall occurrences. The three states were defined as light, when rainfall amount ranges from <60mm/24 24="" 60="" 180="" when="" rainfall="" amount="" ranges="" from="" hr="" and="" is="">180mm/24 hr. To derive the transition probability matrices the method of maximum likelihood was used in the estimation of the transition probabilities. Data on daily rainfall from nine (9) synoptic weather stations were considered. Factors such as month, station and Sea Surface Temperature anomalies (Ssta) were considered to analyze the estimated transition probabilities. To understand and explain the variability that might be present in the estimated transition probabilities the analysis of variance using the Generalized Linear Models (GLM) procedure were performed.
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The analysis of variance approach was used to determine the significant factors that might explain the estimated transition probabilities. Based on the results of the analysis of variance using the GLM procedure of the Statistical Analysis System (SAS), it was noted that for light-to-light transition no factors were found to significantly affect its occurrence. For the light-to-moderate, light-to-heavy, moderate-to-light, moderate-to-moderate, moderate-to-heavy, heavy-to-light, heavy-to-moderate and heavy-to-heavy the factor SSTa was found to have significant contribution in their variability. Aside from SSTa, month and station appear to be significant factors to consider in explaining the variations in the following transitions light-to-moderate, light-to-heavy, moderate-to-light, moderate-to-moderate and heavy-to-light. For the transition moderate-to-heavy the factor station, aside from Ssta, was found to significantly affect its variability. For heavy rainfall occurrences preceded by moderate rainfall occurrences the factor month was also found to be significant.
Roberto T. Rivera
The sensitivity of the characteristic features of the sea breeze to model parameters were not thoroughly documented in the past as these were largely conducted within the context of a much broader study. This is in sharp contrast to past sea breeze studies which are functions of the environmental parameters. Two model parameters which are quite sensitive in the mesoscale are surface friction and ice microphysics. Their greatest impacts are manifest on the systems intensity. A two-dimensional, nonhydrostatic and compressible formulation of the ARPS (Advanced Regional Prediction System) model is developed to examine the net effect on sea breeze intensities of an ice microphysics and surface friction. A control simulation is first done to serve as benchmark and is followed by two sets of experiments. The first set includes ice in its microphysics parameterization and the second set includes a series of simulations in which the surface momentum drag coefficient is varied from 0.08, 0.04, 0.02, and 0.005. The results of these experiments are compared to that of control simulation. The characteristic features which are compared are the distribution of the horizontal and vertical velocities as well as the horizontal divergence. The inclusion of ice, as expected, strengthened the entire sea breeze circulation but rather than occur in most of the semi-diurnal cycle, this intensification was cut short. The resulting sea breeze layers towards the end of the integration period are comparatively weaker. Increasing the surface friction also increases the negation of surface convergence due to relatively weak flows. Decreasing this value enhances the surface convergence due to relatively strong flows. By simulating some additional friction experiments, it was found that when this is decreased further, there is a certain lower range of values in which the convergence peaks and decline. This suggests that there is an optimum value for friction which maximizes the intensity of the sea breeze circulation. These auxiliary values, however, are far from being too realistic.
Nancy T. Lance
The geographical delineation of flood prone areas in the City Camp Lagoon was discussed. The study area is located at the western portion of Baguio City one (1) kilometer from the City proper and when inundated, eight (8) barangays were affected. The techniques of defining the flood hazard were based directly from recorded inundation areas and actual interviews with the affected communities. The assessment was done by relating the flooding to the primary physical characteristics of City Camp Lagoon utilizing topographical, climatological, geomorphological and geological information of the area. Results showed that the extent and severity of the flooding were aggravated by the geomorphology, surface-water run-off, topography, lack of urban planning, improper drainage and human intervention such as uncontrolled garbage disposal.